As we've seen, groups of young people who take sensible precautions and make conservative decisions make for boring horror films. What we need to see is a lone, doomed, minor character take complete leave of his senses and volunteer to check out a suspicious noise. It happens all the time, as this supercut from Slackstory shows.
Along the same lines, if you want to find something in the dark, you need to split up your group -otherwise you'll all be killed at once and the movie would be too short! Although in a few of these clips, I can almost imagine the one suggesting that two people "split up" might really just want to get away from their annoying partner. -via Laughing Squid