>>212632777
When Marty tells the Doc he's from 30 years from now (1955) the Doc says, " my goodness I invented something that actually works and I am still alive in 30 years from now".
He was worried he was going to kill himself but seeing Marty and knowing he would be friends with him in 30 years time and gave him hope and he continued on.
Bloody hell that is poignant, makes me sad thinking about it everytime.