After his company failed, the Once-ler starts regretting every single thing he did and sees himself as a failure: to his family, to the Lorax, to the animals, to Pipsqueak…to himself.
He then thinks he's better off dead and tries to take his own life by walking into a train, but didn't go through with it because he had second thoughts.
Hope.
That was the thought, right?
He had hope that someone won't repeat the same mistakes he did with Greed and Pride, his two deadly sins.
So as an old man, he gives the last known seed to Ted.
