I’ve broken several iPhones including one the same day I got it. The breaks always seemed to happen randomly. Relatively low impact. But once I dropped one, tried to grab it, and ended up flinging it up and across the room where it hit the wall about ten feet up then fell anyway... it was fine. Another time I was hiking and stupidly had my phone out. I fell, landed with the screen side down beneath my hand onto pebbles... not a scratch.

Anyway... I always buy a case now.