BT Men 77a(28) :כי היכי {כי} דלא לימטייה רווחא זיינא זיינא היא דלא למטייה רווחא לא בעי‏ : so that his profit should not turn into a loss for him. Is (the purpose of the law) that he should not incur a loss? Does he not need (to make) a profit?
See the entire entry for zyān, zyānā n.m. loss