I totally understand. This happens when antique shopping (or junk store hopping LOL). I would see something that I loved and decide to have a 'cool down' period and, if I still liked it I would go back to get it...often it would be gone...then I would have a big case of "Buyer's Regret".
I'm finding that happens with fabric as well. See something, do a cool down, go back...not enough or completely gone. yep...Buyer's Regret.