optimism

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.".

   See also {Lubarsky's Law of Cybernetic Entomology}.