9 Developer Mistakes I Stopped Making After Mentorship From a Senior Engineer

One good mentor saved me from years of bad habits.

9 Developer Mistakes I Stopped Making After Mentorship From a Senior Engineer

I thought I was a pretty solid developer.

I could ship features fast, write working code, and even refactor without breaking everything (most of the time). But it wasn’t until I worked closely with a senior engineer that I realized how much I didn’t know — not just about code, but about how to be a developer.

This mentorship transformed the way I approached engineering. It wasn’t about learning new tools — it was about unlearning bad habits. Here are nine mistakes I used to make, and what I do differently now.

1. Writing Code That Works — Not Code That Lasts

Then: My focus was on getting things to work. If the feature passed QA, it was good enough.

Now: I ask: Will this be readable and maintainable six months from now? I learned to write for humans first, machines second. That means using clear naming, proper structure, and avoiding clever hacks that only I can understand.

2. Avoiding Documentation Because “The Code Explains Itself”

Then: I thought comments and docs were optional. After all, wasn’t clean code supposed to be self-documenting?

Now: I understand the power of good documentation — not just in READMEs, but in thoughtful inline comments that explain why, not just what. The best codebases tell a story. I try to leave clues for the next developer (often me) to follow.

3. Solving Problems Before Understanding Them

Then: As soon as I saw an error, I’d start coding a fix.

Now: I pause. I dig deep. I reproduce bugs methodically and read the stack trace like a detective. My mentor drilled into me: Don’t just fix the symptom. Find the cause. Slowing down made me faster in the long run.

4. Overengineering for Imaginary Future Use Cases

Then: I’d build overly abstract systems with the idea that “we might need this later.”

Now: I embrace YAGNI — You Aren’t Gonna Need It. My mentor showed me that simple, focused code is more valuable than a Swiss Army knife of premature abstractions.

5. Skipping Tests to “Save Time”

Then: I saw testing as something to do after development — if there was time.

Now: I write tests with development. Not always TDD, but often close. I’ve seen firsthand how a solid test suite saves hours of debugging and gives the confidence to refactor without fear.

6. Ignoring Code Reviews (or Taking Them Personally)

Then: I’d rush through reviews or get defensive when receiving feedback.

Now: I treat code reviews as learning opportunities. I don’t just address comments — I reflect on them. I also try to leave thoughtful reviews for others, because mentorship goes both ways.

7. Not Asking for Help Soon Enough

Then: I’d spend hours (or days) stuck on a problem because I wanted to prove I could solve it alone.

Now: I still struggle first — but I set a time limit. If I’m stuck for more than 30–60 minutes, I reach out. Asking for help isn’t weakness; it’s efficiency. My mentor taught me that real pros know when to raise their hand.

8. Chasing New Tech Instead of Mastering the Fundamentals

Then: I was constantly jumping to the next shiny thing — new frameworks, languages, libraries.

Now: I invest in depth over breadth. I learned to really understand things like HTTP, databases, concurrency, and clean architecture. Tools come and go, but the fundamentals stay relevant.

9. Not Thinking Like a Teammate

Then: I wrote code that worked for me. I didn’t consider how others would use or extend it.

Now: I write code as part of a team. That means following conventions, adding helpful comments, and building empathy for whoever will maintain this code next. I stopped writing “my” code and started writing our code.

Final Thoughts

Mentorship didn’t just make me a better developer — it changed how I think.

It made me realize that seniority isn’t about knowing everything. It’s about knowing what matters, and being deliberate with your time, your tools, and your team.

If you’re early in your career, find a mentor. If you’re further along, be one.

And remember: Every line of code is an opportunity to grow — if you’re willing to learn.

If you enjoyed this post, follow me for more reflections on software, mentorship, and the journey of becoming a better developer.