(It’s Cmd-O, or Cmd-down-arrow.)

Hitting “enter” to open a file makes it too easy to do it accidentally. What if I didn’t mean to start up a huge app like a pro video editor or something, which takes five-ten seconds to start up?

Cmd-down-arrow is pretty darn easy to invoke from the keyboard, but not so easy that you risk opening a file you didn’t mean to.