Well, it's just most likely, I guess.
I don't think Occam's razor is a proven thing, it's an axiom - something most people choose to agree on as a starting principle.
Think of it this way, if I go into DS1's room, and his books are all over the room, the simplest explanation is, he did that. But it's possible that aliens came in, threw them all over. Or gravity stopped working for a while, and the books just floated around. There are lots of reasons. But the simplest one is, he did it.