The self radical is a bit modified, with things sticking out, but that’s because it’s falling down a slide.
Sure, it’s yourself who’s tumbling down the slide… at least that’s how it feels to you. Who are you? What are you? All you know is you’re somebody, but you don’t know who that somebody is.
You’re falling down this metaphorical slide… And then you hit somebody… and you hit them really hard. On your metaphorical shin (しん). You split it in half and it’s at a right angle. The pain is incredible (shins have a lot of nerves!). It may have been broken, and you may not be able to walk correctly again… metaphorically speaking, that is.