Comment by cheepin

Or you can call map_err to do an on-the-spot transformation if you don't have a general way to go from Error A to Error B.

I still sometimes make mistakes reading rust code with the ? at the end of the line, but it's just a question of what type is it and does the line return. Both of which are handled by the compiler in the end, so you get a little bit of extra knowledge that even if you misread the line of code, there's often limits to how much damage you can cause.