What is the WORST mistake you can make as a programmer?

Question

I'm curious...

Answer 1

To think you can program when you never created an actual big scale program.

Answer 2

my mistake is to build a virus. i run it instead of building it. it crashes my os .

virus was :
it hides on background and create another process of it self in each second.

my os crashed within 2 min.

Answer 3

rm -rf