In 2025, I learned that the distance between a junior Engineer and a lead is measured in the mistakes you stop making. It was a year of challenging product launches and pivots that changed my technical philosophy. I didn't just ship code; I paid the cost of admission in the form of technical debt and manual labor.
That's when I learned that efficiency is a business strategy, not just a technical preference. Here are the major mistakes I made during my professional career in 2025.
1. Poor Communication with Stakeholders
I once told a Product Manager:
"I’ve configured the NGINX reverse proxy to support 5MB image uploads."
Technically true, but useless to them.
As you grow, your job shifts from writing code to solving business problems. Stakeholders don't care about the how; they care about the result.
The Shift:
Junior: "I updated the NGINX config."
Lead: "Users can now upload high-res images. The marketing bottleneck is gone."
It's the same as when you play a guitar solo. Of course you're not going to tell people the fancy scale you're using. They only care about the feeling.
Stakeholders care about results and making the product better, not much about the fancy tech you use.
2. Infrastructure as Manual Labor
If your "deployment process" involves opening pgAdmin to manually add users, or if your documentation is a list of 20 manual steps to configure a server, you’ve fallen for the Sysadmin Trap.
It's the same when you have to set up the entire AWS architecture using raw dashboards.
You are acting as a manual gatekeeper instead of an architect.
Manual steps are invitations for human error. If you have to "remember" to set a config variable or manually assign a role to a new team member, you haven't built a system but a bottleneck.
The Shift:
Junior: Manages the database and servers through a GUI (pgAdmin/AWS Console) and manual docs.
Lead: Automates the environment. Use Migration Scripts to manage roles and Ansible/Terraform to define infrastructure.
The business shouldn't depend on your memory to set things up. It should depend on your code.
3. Configuration Overhead
Rebuilding a Docker image just to change a URL is a failure of architecture.
I’ve seen it happen: a stakeholder decides to change a domain or an API endpoint, and the engineering team has to trigger a full CI/CD pipeline, wait for the build, and redeploy everything for a single string change...
You should never have to rebuild your code to change how it behaves in its environment.
The Problem: Hardcoding Behavior
Whether it's a "feature flag," a timeout limit, or a third-party URL, if it's baked into your source code or your Dockerfile, your system is rigid. Rigid systems break under the pressure of fast-moving startups.
The Shift:
Junior: Hardcodes "minor" settings or bakes them into the Docker image during build time.
Lead: Uses Environment Variables and Secrets Managers (like AWS Secrets Manager or Parameter Store).
Ensure that the Docker image is immutable. It should be the exact same image in Staging as it is in Production. The only thing that changes is the environment it plugs into.
This doesn't just save time, it saves the business from deployment fatigue and unnecessary downtime.
4. Poor Testing Strategies
If your "Testing Strategy" is just you clicking around the UI before a deploy, you don't have a strategy, you have a prayer.
I once saw a production launch stumble because a user couldn't use a "dot" in their username. It sounds small until it’s the reason your conversion rate drops by 15% on launch day.
You need to set up testing from day one and let your CI/CD pipeline be the "bouncer" that keeps bad code out of production.
What Actually Matters (The 80/20 Rule):
You don’t need 100% code coverage. That’s a vanity metric. You need to protect the Critical Path:
Permissions & Validations: Can a user see data they shouldn't? Can they sign up with valid characters?
Critical Business Logic: Does the checkout work? Does the subscription upgrade trigger correctly?
Edge Cases & Race Conditions: What happens if two users click "buy" on the last item at the exact same millisecond?
The Shift:
Junior: Tests manually and hopes for the best. Thinks tests "slow them down."
Lead: Uses Unit Tests for logic, Integration Tests for the database/API flow, and E2E for the "happy path."
I know that tests aren't about finding bugs; they are about confidence. They allow the team to move fast without the fear of breaking the product every time they push code.
Set standards when writing tests and ensure your team is proactively working on them as well.
5. Poor Permission Management
I still remember these checks as a form of technical debt:
if (user.role === 'admin') {
// Execute logic to ban user
}
This is fine for an MVP. But as the system grows, combining business logic with hardcoded roles becomes a nightmare.
The Problem: Role Inflation
Imagine we're building a social media platform. Initially, Admins ban users and regular Users view posts. Simple.
Then the business scales. You introduce a Moderator role. They need to manage reports and suspend accounts, but they shouldn't have full Admin access to the billing system. Suddenly, your code looks like this:
if (user.role === 'admin' || user.role === 'moderator') {
// Execute logic to suspend account
}
Now imagine this check is scattered across 50 different files. If the CEO decides to add a "Junior Moderator" with limited powers, you have to tweak every single if statement. Congrats, now you're fighting with your own system.
The Shift: Ability-Based Access
A Lead Engineer stops thinking about who the user is and starts thinking about what they are allowed to do.
if (ability.can('suspend', 'User')) {
// Execute logic
}
The Transformation:
Junior: Checks the "ID card" (Role) at every door.
Lead: Implements a "Keycard System" (Abilities/Permissions).
By using a library like CASL or a specialized Policy class, you decouple the business logic from the organizational hierarchy. When the business pivots or adds new roles, you change one configuration file, not the entire codebase.
And by the way, your tests will be simpler and auditing your permissions is a walk in the park now!
6. No Seeding Strategies
I used to spend 20–30 minutes manually clicking through the UI, creating fake accounts, and spamming forms just to get "real-world" data to work with.
I was doing the work of a script, but manually.
Seeding is the process of populating your database with a predictable set of data for development and testing. Without it, you aren't engineering; you're just messing around.
Why Seeding is a Business Strategy:
Handling Edge Cases: You can instantly recreate that one specific, weird bug that only happens to users with 50+ transactions and an expired subscription.
Stress Testing: You don't need to "spam" the system. One command generates 100,000 records to see if your PostgreSQL queries or Redis cache actually hold up.
Instant Onboarding: A new engineer (or a collaborator) should be able to clone the repo, run one command, and have a fully functional environment.
Testing the "Golden Path": Imagine you are debugging business logic for premium subscribers. Every time you want to test a change, you have to manually trigger a Stripe checkout, click through 5 different screens, and wait for webhooks. That's 10 minutes of manual labor per test. A seeding script handles this in 2 seconds. If you don't automate your state, you aren't testing; you're just doing expensive data entry.
The Shift:
Junior: Manually creates "test_user_123" every morning.
Lead: Automates the state of the world.
If you don't have a seeding strategy, you’re wasting the company’s most expensive resource: your time.
7. The "Hard Delete" Sin
In a startup, data is the only asset you can't recreate. I used to think that DELETE FROM was just part of the CRUD flow. I was wrong.
A hard delete is an irreversible loss of business knowledge. If a user deletes their account today, but the CEO wants to know why churn increased six months from now, that data is gone. The business no longer has access to the history.
The Shift:
Junior: Deletes records to "keep the database clean."
Lead: Implements Soft Deletes (deleted_at timestamps) and Audit Logs.
Yes, it's kind of tedious to only update a flag. However, it's critical for audit purposes and compliance.
8. Thinking a Company Was Going to Save Me
This was the hardest lesson of 2025. I spent too much time being reactive, waiting for a "safe" job or a promotion to change my life.
I realized that my security doesn't come from a contract; it comes from my reputation, my Network, and my skills.
The Shift:
Junior: Waits for instructions and a paycheck.
Lead: Acts as a business ally. I treat every project like I’m a partner, and I focus the most on my own knowledge and skills.
TL;DR — Engineering Maturity Checklist
- Communicate outcomes, not configs: Stakeholders care about results, not technical steps.
- Automate infrastructure (IaC): Use Terraform/Ansible; don’t be a manual gatekeeper.
- Keep configs flexible: No hardcoding; rely on environment variables and secrets managers.
- Test for confidence, not coverage: Protect the critical path with unit, integration, and E2E tests.
- Design permissions with abilities: Move beyond role checks; implement ability‑based access control.
- Seed your environments: Automate realistic data for onboarding, edge cases, and stress testing.
-
Preserve data with soft deletes: Use
deleted_atflags and audit logs; never throw away business knowledge. - Own your growth: Security comes from skills, reputation, and network — not contracts.
About 2026 and the Future
If you’ve made it this far, thank you for reading! :)
I wish you a Merry Christmas and a productive New Year with your family; of course, if you celebrate it.
To start 2026 right, I’m currently diving into The Pragmatic Engineer. My goal is to become a more effective leader for my team and to ship features that are not just fast, but reliable.
I’m also returning to pen, paper, and whiteboards. I’ve realized that relying too much on AI and digital tools made me drift. There is no substitute for the clarity of drawing a system by hand before writing a single line of code.
Talk to other engineers outside your startup, rest, and plan your days. This is a marathon, not a race.
Here’s to a year of less entropy and more architecture.
What was your biggest lesson in moving from Junior to Lead? I'd love to hear from you.
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