one swallow doesn't make a summer

one swallow doesn't make a summer

  (British & Australian)
something that you say which means because one good thing has happened, you cannot therefore be certain that more good things will happen and the whole situation will improve Okay, they won their last game but one swallow doesn't make a summer. They're still bottom of the league.
See also: make, one, summer, swallow
References in periodicals archive ?
One swallow doesn't make a summer, they say, but in the midst of the dol-drums, how many fine ballerinas does it take to give a festival wings?