Coincidences do occur in real life. And if you’re writing, say, a paranormal, where you have a curse or a spell or some object that keeps landing in the possession of brides left at the altar, that is one thing. The coincidences are part of your world-building.
But if you need to have a scene between the hero and heroine, so you have them run into each other at the grocery store, and then at the post office, and then in an elevator, and then at a ballgame … ugh, ugh, ugh. If your character is trying to solve a mystery, and she keeps stumbling on clues by total dumb luck, another triple ugh.