Bad luck can't hurt you in the long run. But if you start to play worse because of it than it can. I had a badluck streak 2 days ago for about 800 hands. I never hit sets, lost witch my pocket Aces and if I had a hand everyone folded. After that 800 hands I semi-tilted and started playing to many hands.
I lost 7 buyins of witch only 3 to bad play. But I cold have avoided those 3 if I stopped earlier.
So if you like me start to play a bit worse after some badluck it might be better to stop before this happens.
badluck streak+ even a tiny bit of tilt= big losses.