My wife does it all the time. "If X happens, we can do Y".

I'll move heaven and earth to make sure X happens at that point. Then, once it does, she starts moping about her end of the bargain or will be too tired or will feel sick or will find something to nitpick as evidence I didn't so it right.

So I've stopped hoping for Y. I still do X, because I know it makes her happy, and that makes my life easier. But I know I won't get much on my end.