I always felt like Yoda was testing Luke by being impatient with him. And like the trial he faced at the force cave he failed.

He also has some doubt that Luke would complete his training because of him being the son of Skywalker.

Luke is a bit of a hothead. Very impulsive and brash.

He is Anakin’s son through and through. Much anger in him like his father.

Kenobi seems to be the one who thinks Luke has the potential to defeat Vader and the Emperor, the same kind of pride that Kenobi felt over Anakin which led to him becoming Darth Vader.

Yoda knows Luke could easily fall to the Dark Side and into the clutches of Palpatine, and suffer his fathers fate.