Well that will be an exception, though it depends on what's the odds of the bug showing up on the particular day.
It had happened with me when after a successful (rather awesome) demonstration of our project, just going through the code, I found a very deep-hidden bug in code which could have wreaked havoc on us. But it seems luck was with us on that day. We also tested our system under various conditions too many times but the bug never showed up.

So you can say that if a system works 99% of time, there's only 1% chance that it wouldn't work on a given time, atleast on statistical grounds. That risk is well worth taking for a lazy student who would never wish to go through heavy documentations & books & all that just to find that 1-percent-time-occuring bug. It's almost equivalent if he never knew about it.

Consider this: if a project vendor offers a student a great & impressive project but tells him that it works only 99% of time & demonstrates to him, (say, hypothetically) 1000 times, of which almost 990 times it works, would he just sit down & start debugging it?

your future employer should, you wrote unrelible code and may do that again.

Well I was particularly talking the case of lazy college goers. If they had to show the code to their employer, even they would sit down & start debugging it!!!