Despite not being a professional programmer, i use python or c to accomplish simple tasks.

Once I needed a nasty equation to use with various data for physics lab. I thought that it would take a few hours if i used some mechanic calculator. Then i've written a python script to make things easier but something was wrong.

After finding my mistakes one of which was forgetting to put ":", i realized that it had already took 2-3 hours, not to mention inventing satanic arithmetic techniques since i thought the errors was caused by my math :)

Sometimes when you don't see it, you don't see it!

Now i can find the syntax errors without thinking for a moment :)

Any similar annoying mistakes that you've experienced?