I wrote this unfinished sentence in March 1989. I was impressed with the answers it received, so I asked different participants for their responses in March 1992:
One is a full-fledged actor only when...
...one is able to convince oneself that a lie is the truth. (Jenni S.)
...you actually succeed and convince the officer that you were only driving 86 in a 25 mph zone so you could get to the hospital before your beloved grandmother passes away. (Keith T.)
...the director of a play or movie has to recast because the actor/actress has died. i.e. You are an actor/actress until you die. (Jonathan L.)