Staying in the same position for too long.
It was my first "real" job in 2007 after graduating college in 2005, but had been working on the web since 99. I received one promotion from web developer to software engineer and then stalled for a number of years in the same group. I should have switched teams sooner. I missed out on a lot of opportunities.
I've seen this in many first programmers, they stick with their first job a long time. I encourage people to switch jobs early to ensure they get a feel for what is out there.
The main issue I ran into is that when I took the job it was such a huge jump in pay that I didn't realize I was at the very bottom of the pay scale for my position. I undersold myself because I moved from a three person shop to a huge corporation.
My big take away was if you're not moving to a new position every two years at least look for something new inside your company. Staying in one place will not help you.
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