programming fuck ups

What's the biggest screw up you ever made writing software?  Once a team I was on overshot a DCUT for some datacenter automation tools by two weeks, and it still ended up being shitty because the customer kept wanting to add shit.

This is especially dangerous in python since

while (...):
   do this1
   do this2
do this3

is not the same as


while (...):
   do this1
   do this2
   do this3