In Czech, “to teach” is učit “to learn” is učit se which, although it doesn’t seem like the czechs think of it this way, translates as “to teach myself”. Likewise, půjčit means “to lend” while půjčit si means “to borrow”. There is a very appealing symmetry there. Apparently “lend”, “borrow”, and “return” in English forms an inscrutable quagmire for the native czech.
When the verb is accompanied by se, it is an indication that the action of the verb is being reflected back onto the speaker. Si, on the other hand, indicates that the action is being applied to another object.
When you get to washing, this becomes interesting. You can say, míju – “I wash” – but that applies strictly to the general act of self-cleaning. When you are washing your hands, Míješ si ruce you are washing some external object. Your hands are not you. Built into the language is a separation of the parts and the whole. You could name any part: heart, brain, foot, and that part is not you. It’s not even part of you. It is something separate, an object you interact with the same way you would with a stone.
And there you have, built into the Czech language, a distinction between the whole and the parts.