The Fifth Beatle

"You have a collect call from England.  Will you accept?"
"Who's calling?"
"Sir Paul McCartney."
"Sir Paul's calling collect?"
"Yes, ma'am."
"Okay, put him through.  Hello?"
"Is this the Short Jewish Gal?"
"Who wants to know?"
"This is Sir Paul McCartney."
"How do I know it's really you?"
"You'll just have to trust me."
"Name the other members of the Beatles."
"Sam, Max and Jacob."
"What can I do for you, Sir Paul?"
"I understand you've been telling people you're the 5th Beatle."
"Is that a problem?"
"Yes."
"Why?"
"You're not the 5th Beatle."
"I'm not?"
"No."
"If not me, then who?"
"That's for me to know and you to find out."
"Give me a little hint.  I won't tell anyone."
"No."
"Is it Yoko?"
"No."
"Brian Epstein?"
"No."
"Mick Jagger?"
"No."
"Then it might as well be me."
"It isn't."
"Then who is it?"
"I'd rather not say."
"But Sir Paul, don't you understand?  It's just a metaphor.  Everyone feels like the 5th Beatle sometimes. The one on the outside looking in. The one who's close to the action but not part of it.  The one who didn't quite make the cut."
"When you put it that way, welcome to the group.  Do you play any instruments?"
"Left-handed guitar."
"Sorry, that spot's already taken."