Yes, and even a genuinely (with perfect play) losing position can win if it sharp enough and causes your opponent to make a mistake! There's also just the relative strength of one branch vs another - have to prune some if there are too many.
"The Contempt Factor reflects the estimated superiority/inferiority of the program over its opponent. The Contempt factor is assigned as draw score to avoid (early) draws against apparently weaker opponents, or to prefer draws versus stronger opponents otherwise."
Imagine that there was some non-constructive proof that white would always win in perfect play. Would a well constructed chess engine always resign as black? :P
I was just trying to give the flavor of it.