Isn't sharing supposed to be willingly letting someone use something instead of keeping it all to yourself? Because that is so no how it usually goes down.
1. The "Want" stage
2. the pretending stage.
you know, the one where you pretend to ask nicely just so that if your parets come and ask, you can say you didn't skip right to yelling.
you had it all planned from the beginning. you will have the object in question no matter what it takes. there is no other option. the toy is YOURS.
3. the yelling stage
the trouble is, now comes
4. the intervention stage.
that one where the parents have finally realized something is going on and they are coming to intervene and get to the bottom of things.
4. the selfish stage
you do everything you can to make the other person look selfish, because maybe, just maybe, you can guilt them into taking the toy from the other person and giving it to you. you already have your "asked nicely" defense.
5. the no one gets it stage