When Brother didn't think that Doodle was trying to walk, how did brother try to motivate him?

From the text:

He'd nod his head, and I'd say, "Well, if you don't keep trying, you'll never learn." Then I'd paint for him a picture of us as old men, white-haired, him with a long white beard and me still pulling him around in the go-cart. This never failed to make him try again.