optimism

n.

What a programmer is full of after fixing the last bug and before discovering the next last bug. Fred Brooks's book The Mythical Man-Month (See Brooks's Law) contains the following paragraph that describes this extremely well:

All programmers are optimists.  Perhaps this modern sorcery especially
attracts those who believe in happy endings and fairy godmothers.  Perhaps the
hundreds of nitty frustrations drive away all but those who habitually focus
on the end goal.  Perhaps it is merely that computers are young, programmers
are younger, and the young are always optimists.  But however the selection
process works, the result is indisputable: This time it will surely
run, or I just found the last bug..