Most of these are not true, or are not true in the way expressed. Sometimes there are actual blooper takes included in films, but it’s rare. Even if there is a blooper and it turns out to be better, the director gets the actors to recreate the superior-by-accident blooper for many takes for better camera position or to really nail it.

This is mostly lies and is not the way high-budget films work. Even “improvised” lines and scenes are re-shot many times almost without exception.