Who said "There's no way I can do this by myself."?

This quote is attributed to Marty McFly.

There's no way I can do this by myself. - Marty McFly

"There's no way I can do this by myself."

Marty McFly

"This is heavy."

"There's that word again, 'heavy.' Is there something wrong with the Earth's gravitational pull?"

"I'm your density. I mean, your destiny."

"You're my best friend, and I care about you, but don't ask me to do this."