What happens when you can't remember your lines?

It's your job as an actor to remember your lines.

Some are good at doing improv if they slip up, but they keep it natural looking.

Sometimes directors like a good ad-lib

depends,..if you're old, they give you cue cards,...

Marlon Brando never learned his lines,..(supposedly) to keep things spontaneous.

I guess it depends on how valuable you are to the film,...your box office draw, or whatever.

Marilyn Monroe kept messin' up her lines on this one flick & got fired,...for bein' drunk or late or somethin'.

There's many actors who never remember their lines at first lol no they won't get fired unless they never learn them.