I'm going to tell my friend forget his goals and ambitions.
Why would you say that to your friend?
Because it's the foolish kind of thing he does, why would he waste his time on that?
Discouraging your friend will lead to negative outcomes. When you motivate someone, they end up confiding in you. This will make them trust you and you may earn some good friends in the long run.
Why should I encourage someone like him?
Because he's your friend. You should be lifting him up, not discouraging him from obtaining his goals.