bad things come in threes (unfortunate events usually occur more than twice) / good things come in threes (fortunate events hopefully occur more than twice)

one swallow does not a summer make

a bad penny always turns up

(humorous) look who's here!

blood is thicker than water

(idiomatic, euphemistic) where the sun don't shine

(idiomatic) Alternative form of non sapere che pesci pigliare

(idiomatic) to be unable to find possible inroads or solutions to a problem; to be at a loss for what to do

in the twinkling of an eye, in a flash / at the drop of a hat

don't say a word