[karmakaze]

I also found this to be defeatist (and the basis of the post):

> As a programmer, it’s impossible to predict all the states that your program can end up in.

It's true that we can't predict all the things other programmers will change the program to do in the future, but we can take precautions such as rejecting invalid states, or if being liberal in the input it accepts transform it to something usable.