The Bug Wasn't in the Code. It Was in My Assumption.

Sometimes you spend an hour looking at a piece of code, convinced that something complicated must be wrong. You check the logic. You check the database. You add print statements. You restart the application. You question your entire career.

Then you discover the problem.

Your assumption was wrong.

Not the algorithm. Not the programming language. Not the framework.

You simply expected something to behave differently from how it actually behaved.

I have started noticing that a lot of debugging is really just this: finding the assumptions hiding inside our code.

We make assumptions all the time

When writing software, we have to make assumptions.

We assume a value will exist.

We assume a user will enter the correct format.

We assume a database query will return a result.

We assume an API will respond successfully.

We assume a file will be where we expect it to be.

We assume something that worked yesterday will still work today.

Most of these assumptions are reasonable. The problem starts when we forget that they are assumptions.

For example, imagine you write:

name := getUserName()

fmt.Println("Hello", name)

You might look at this code and think, "That's fine."

But what happens if getUserName() doesn't find a user?

Maybe it returns an empty string.

Maybe it returns an error.

Maybe it returns a default value.

The code itself might be completely valid. The problem is that you assumed getUserName() would always give you a name.

This is where bugs become interesting.

The code is doing exactly what you told it to do.

You just didn't tell it what to do in every situation.

"It works on my machine"

This is probably one of the most famous sentences in software development.

"It works on my machine."

And sometimes it genuinely does.

You test your application locally. Everything works. You push your changes, someone else runs the project, and suddenly something is broken.

At first, it is tempting to think, "What did they do differently?"

But that question can hide another assumption.

You assumed your environment was the same as theirs.

Maybe you had a different version of Go installed.

Maybe your database already contained some data.

Maybe an environment variable existed on your machine.

Maybe you had a file locally that wasn't committed to Git.

Maybe your application depended on something that you didn't realize was installed.

The code didn't necessarily change.

The environment did.

That is why developers use things like environment variables, dependency management, containers, configuration files, and reproducible builds.

They help reduce the number of things we silently assume.

APIs are another good example

When working with APIs, it is easy to assume that a successful request will always return the response you expect.

You send a request.

You get a response.

Everything is good.

Until the API returns an error.

Or an empty response.

Or a different status code.

Or the service is temporarily unavailable.

Or the request takes longer than expected.

If your application only handles the "everything went perfectly" situation, it might work beautifully during testing and fail when a real user interacts with it.

The important question becomes:

"What else could happen?"

Not because we expect everything to fail, but because reliable software is built around handling the situations we didn't expect.

Databases can expose assumptions too

Databases are another place where assumptions can quietly cause problems.

Suppose you expect a query to return exactly one record.

You write your code around that expectation.

But what if there are no records?

What if there are multiple records?

What if the data is NULL?

What if someone deleted the record between two operations?

Again, the SQL query might be correct.

The problem is the expectation surrounding it.

This is something I have found especially important while working on back-end projects. When you are dealing with users, transactions, and stored data, you cannot simply assume that everything will always be in the state you expect.

You have to check.

Question the assumption

One of the most useful changes in my approach to debugging has been learning to ask simpler questions.

Instead of immediately thinking:

"What complicated thing is breaking?"

I try asking:

"What am I assuming here?"

What value do I think I have?

What value do I actually have?

What do I think this function returns?

What does it actually return?

What happens if the value is empty?

What happens if the request fails?

What happens if the user does something I didn't expect?

What happens if the database doesn't contain the record?

These questions can sometimes solve a problem faster than staring at the same five lines of code for twenty minutes.

The computer isn't always the problem

This is probably one of the biggest things I am learning as I continue building software.

When something breaks, my first instinct used to be to look for something complicated.

Maybe there is a bug in the framework.

Maybe I misunderstood the language.

Maybe the database is doing something strange.

Sometimes that is true.

But sometimes the explanation is much simpler.

I thought a value was one thing, but it was another.

I thought a function was being called, but it wasn't.

I thought the database contained a record, but it didn't.

I thought the request succeeded, but it returned an error.

I thought my code handled a situation, but I had never actually tested that situation.

The code wasn't necessarily "bad."

My understanding of what was happening was incomplete.

And that distinction matters.

Good debugging isn't just fixing code

I used to think debugging was mainly about finding the broken line and changing it.

Now I think it is more about finding the gap between what I believe the program is doing and what the program is actually doing.

That gap is where many bugs live.

Sometimes the solution is one line of code.

Sometimes it is adding an error check.

Sometimes it is changing a database query.

Sometimes it is reading the documentation instead of guessing.

And sometimes the solution is simply realizing:

"Oh. I assumed that."

That might be one of the weirdest parts of programming.

The computer is usually not confused.

We are.

And that's not necessarily a bad thing.

Every wrong assumption is an opportunity to understand the system a little better.

So the next time you spend an hour debugging something that seems ridiculously complicated, try stopping for a moment.

Before rewriting everything, ask yourself:

"What am I assuming is true?"

You might find that the bug was never hiding in the complicated part of the code.

It was hiding in something you thought was obvious.