10 Coding Mistakes That Could Cost You Your Job – And How to Avoid Them

Even experienced developers fall into common traps that can delay delivery, introduce bugs, or damage their reputation. Some of these mistakes may seem harmless, but they can pile up and cost you your job or your freelance clients.

In this post, we’ll break down 10 critical coding mistakes with real-world insights and simple solutions so you can code smarter, faster, and safer.

1. Not Using Code Comments

What’s the big deal?

Imagine opening a project from six months ago and seeing 500 lines of code with zero comments. 

You're lost, frustrated, and wasting hours just trying to understand what your past self was thinking.

Why it matters:

1.  Makes code easier to read and maintain

2.  Helps team members understand logic

3.  Aids debugging when you return to old code

Example:

A junior developer, once forgot to comment a complex payment algorithm. A new team member misinterpreted the logic and introduced a bug that cost the company a week of development time.

Solution:

Write clear and purposeful comments, especially around complicated logic. It's not about explaining what the code does, but why it does it.

 

READ ALSO:

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2. Skipping Testing

You may think your code works perfectly, until it breaks in production.

Why it is important:

1.  Prevents hidden bugs

2.  Ensures new updates don’t break old features

3.  Builds confidence in your code

Pro tip:

Automate your tests using frameworks like Jest, PyTest, or JUnit, depending on your stack.

Quote to remember:

“Code without tests is broken by design.” – Jacob Kaplan-Moss (Django Co-founder)

3. Copying and Pasting Code Blindly

It’s tempting to grab a snippet from Stack Overflow, paste it in, and move on. But that’s risky.

What can go wrong?

1.  Introduces security flaws

2.  Breaks your app because you don’t understand the logic

3.  Makes debugging harder

Example:

Imagine a dev copied a login system without checking password handling. It stored passwords in plain text. The app got hacked.

Fix:

Read, understand, and test every line you copy. Make it your own.

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4. Ignoring Version Control (e.g., Git)

Still using ZIP files to store project backups? 

Stop. Right now.

Why it matters:

1.  Tracks every change you make

2.  Lets you roll back mistakes

3.  Makes collaboration seamless

Tip:

Learn how to use git commit, git branch, and git revert. 

Platforms like GitHub and GitLab offer free repositories and tutorials.

5. Hardcoding Values

Hardcoding is inserting fixed values like this:

discount = 0.25

Instead, use variables or configuration files so you can easily update them later:

DISCOUNT_RATE = 0.25

Why it is useful:

1.  Keeps your code flexible

2.  Makes changes easier in the future

3.  Reduces errors when scaling

6. Overcomplicating Your Code

Complex code might make you feel smart  but simple code makes you a pro.

Danger signs:

1.  Nested loops inside nested functions inside classes

2.  Unnecessary conditions

3.  Overengineering small features

What to do instead:

Write for clarity. Follow the KISS principle: Keep It Simple, Stupid.

“Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler

7. Ignoring Security Best Practices

What happens when you skip security?

1.  Hackers exploit input fields

2.  Passwords are leaked

3.  Sensitive data is exposed

Simple fixes:

1.  Validate and sanitize all user inputs

2.  Hash passwords (never store them raw)

3.  Keep dependencies up to date

Link to learn more:

OWASP Top 10 Security Risks

8. Failing to Document Your Code

Comments explain the "why", but documentation explains the "how" to use your project.

Why it matters:

1.  Makes onboarding new developers easier

2.  Helps others (and you) use your code correctly

3.  Builds trust with open-source users

Tools to use:

1.  Markdown files (README.md)

2.  Doc generators like JSDoc, Sphinx, or Swagger

9. Not Asking for Help

Stuck on a problem for hours? You’re not alone.

What’s at stake:

1.  Wasted time

2.  Missed deadlines

3.  Frustration and burnout

What to do instead:

1.  Ask a teammate

2.  Post on Stack Overflow

3.  Join coding communities like Reddit’s r/learnprogramming or Discord groups

READ ALSO: 

13 Epic Projects to Try using Python

10. Being Resistant to Feedback

Code reviews are not attacks, they’re opportunities to grow.

Why this matters:

1.  Feedback reveals blind spots

2.  Shows you alternative solutions

3.  Helps you think like a senior developer

Tip:

Say “thanks” for every bit of feedback, even if you don’t agree. Learn from it or discuss it professionally.

 Quick Checklist: Are You Making These Mistakes?

Mistake	Why It's Dangerous	Quick Fix
No Comments	Makes your code unreadable	Add "why" comments
No Testing	Bugs sneak in	Use unit & integration tests
Blind Copy-Pasting	You inherit bugs	Understand every snippet
No Version Control	Can’t recover changes	Use Git with GitHub
Hardcoding	Difficult to update	Use variables/configs
Overcomplicating	Hard to maintain	Keep code simple
Ignoring Security	Vulnerable to attacks	Sanitize & hash data
No Documentation	Confuses others	Use clear READMEs
Avoiding Help	Slows progress	Ask, search, collaborate
Resisting Feedback	Limits growth	Accept, learn, adapt

Avoiding these common mistakes can set you apart in job interviews, freelance work, and team environments.