A student came to see me today looking very serious.   He explained that he got zero for a certain part of the assignment and wanted to know why.   Then he said:

I implemented something different.  Do I actually have to make it do what the specification says?

Ummm, YES!  Hello?  Just what do you think is the point of this entire course?

*Sigh*, I really wish I could actually say that to students instead of just thinking it.