He insists Villa could lift the Capital One Cup this season and still get relegated - because he has been there, seen it and done it.
Foster, who won the Carling Cup with Birmingham two years ago - when they beat Arsenal only to then suffer relegation, said: "Everyone was so mentally drained.
"If you ask any of the Birmingham lads why we got relegated, the cup win really was the main reason. It's mad to think that it could take weeks to get over something like that - but I swear to you it did. After the final, we were awful. And it snowballed from there.
"I still don't think Villa will change it, though.
"If they have a chance to win a first major trophy in a long while, they'll still say 'let's try and do it, then see how we go afterwards'.
"You've got to do that. You'd rather win the cup final and see what happens after."