The general idea is that failure teaches you more than success; succeeding at something means that, at some level, you already knew how to do it. It is of course debatable whether this is true in real life, but I thought I’d experiment with it as a way of making failures less bad for the player.
Why not aim for failure all the time, then? Because failure still has consequences. For instance, early on in your alchemy class you can try to make something that’s very difficult to do. Not passing the check isn’t just a failure, it’s a spectacular failure: It ends up setting off the school’s wards. So even though you learn more about alchemy this way, you (A) don’t get the potion you were trying for (whereas if you’d tried an easier one you’d at least have gotten something), and (B) start getting a reputation for someone who does dangerous things.