Diego is recovering too -- from the accident that put him in a wheelchair and the death of his mother shortly after. The garage apartment is where he's keeping his mother's things, and as long as they're up those stairs and he's down on the ground, there's no way he can deal with his loss. And that's just how he likes it.
Healey believes in science. Diego believes in luck. It will take a blend of both, and some prayer thrown in besides, for these two to learn that it's the journey and the destination that matter.