Im not sure of a formal diagram would be useful here, but lets look for a flaw, or a missing link to make this make more sense.
We are given the definition of PI, and told that it is a skill which does not develop on its own. The author then tells us that if someone were always given what it wants, then it could never have PI. There is a bit of a flaw here- we dont know that being given everything you want would actually inhibit the ability to have PI- maybe something about being given en what one wants would actually help one to develop PI somehow.
So, we are looking for an answer that proves that PI cannot be developed if one is given everything they want. While B is not exactly that, it does explain why being given everything you want would mean that you never develop this skill, so it does plug the gap.