I'd love to know the percentage of programming errors caused by

[Cort Haus]

cutting and pasting similar chunks of code - to 'save a bit of time'. The bits that need changing all get edited - except for one.

Any smart-arse saying that any remotely similar chunks of code should all be optimised into some uber-efficient routine can just kindly **** off. Thanks.

[onodera]

Around 33%, from my experience; 33% are from ignoring edge/special cases and possible exceptions, 33% are brain farts, the remaining single percentage includes everything else.