Today’s saying 28: Opportunity only knocks once
شانس یکبار درب خانه را می زند
Possible interpretation: We should take an opportunity (or chance) when it comes. According to this saying, it will not come again.
Note: knock (verb) = strike or hit (a door) noisily to attract attention | opportunity (noun) = a lucky chance; a set of circumstances that makes it possible to do something