you'd better believe it

you'd better believe it

Also, you better believe it. You may be assured, as in You walk ten miles every day?-You'd better believe it! This imperative is almost synonymous with you bet your ass. [Colloquial; mid-1800s]
See also: believe, better
References in classic literature ?
I don't want to see any father coming home, and you'd better believe it.
Well, you'd better believe it, because New Line is currently making offers to directors on the strength of Depp's interest in portraying the late flamboyant pianist known as Mr.