The rot sets in in ROTJ.
The original shooting script and the novel expands Ben's reason for fibbing to Luke to underline just how important he is and how recklessly futile his rescue attempt of friends was.
By trimming that Ben comes across as manipulative as Palpatine.
Yoda is keen on Luke facing his fears (he never asks Luke to kill his father just face and defeat Vader) but Ben comes across as being obsessed with Luke killing Vader (which is a bit of tall order after using a myth about a pre-existing murderer to get Luke to start his quest in the first place).
Ultimately it's Yoda's approach of NOT DEPENDING ON WEAPONS (I'm looking at you Lucas) that wins the day.
The PT Jedi are a bloody weird bunch.
When I saw ANH and ESB I never for a moment imagined a child procuring, Ninja, Vatican State, UN peace keeping 'force', that turned a blind eye to slavery enforced familial disconnects while obsessing about celibacy.
It turned an epic battle between good and evil into the clash of two slightly different creepy cults and the resulting fallout.
With poopy jokes for kids.