LB – oh, sorry for misunderstanding!
I’m not 100% sure of the origins in the Talmud. But I’m pretty positive that it’s not referring to asking Hashem for things.
If you want to know the context in which I first heard the quote, it was when a friend of mine was telling me about an episode of LA Law that she had watched involving a guy who was refusing to give his wife a get and was making all sorts of demands. And the judge told him, “Tafasta merubah lo tafasta”.
I think the ending was that he got struck by lightning or something like that.
I would guess that perhaps the Gemara is referring either to people who push themselves too far too fast or to people who try to get too much out of other people (like in our case).
But, I don’t know – you’ll have to wait for someone else to answer you.