( saying ) you must not take too seriously a small sign that sth is happening or will happen in the future, because the situation could change
ONE SWALLOW DOESN'T MAKE A SUMMER
Meaning of ONE SWALLOW DOESN'T MAKE A SUMMER in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005