One more thing on that, I found a quote from Vision of the Future (number 2 in the Hand of Thrawn duology by Timothy Zahn) that touches on this.
Page 405
(referring to Mara Jade) "She grimaced. ‘Besides, I keep remembering stories about how the last step to becoming a Jedi is usually making some supreme and rather ugly personal sacrifice. I’m not crazy about that one, either.’
‘It’s not always as bad as it seems,’ Luke said, and Mara could sense his discomfort as unpleasant memories of his own floated back to the surface. ‘Just before he died, Master Yoda told me that before I would truly be a Jedi I needed to face Vader again. I jumped to the conclusion that that meant I had to either kill him or let him kill me. As it turned out, it didn’t happen either way.’
‘But you had to be willing to make that sacrifice if necessary,’ Mara pointed out. ‘Thanks, but I’m not interested.’
‘Then you automatically limit your capabilities,’ Luke said."
This accurately reflects the pre-1999 view of what happened. Before the prequels, this is what the original trilogy actually shows and its interpretation.
To become a Jedi, someone needs to make a final, spiritual sacrifice.
In Luke’s case, he had to face Vader.
Like many viewers, Luke incorrectly assumed that this could only mean a fatal duel to the death and Yoda was sending him to either kill or be killed.
The reality, under the influence of the Force, was more complex than that. Yoda could have foreseen this or known that it was more nuanced, because again it was about a spiritual confrontation for Luke to finish becoming a Jedi, not about destroying the Empire.
However, Luke had to be willing to go through with it, if it did mean kill or be killed, which is what Obi Wan tells him. If he wasn’t willing, he was limiting himself.
Now, the prequels ignored this final sacrifice concept. They might be alluding to it with “the Trials” but the Trials are never explained or shown. Perhaps in Obi Wan’s case it was losing Qui Gon. Either way, after The Phantom Menace, it’s dropped. After the prequels, a lot of people assume that Luke is just on an assassination mission like with Yoda and Obi Wan trying to kill Vader and the Emperor in Revenge of the Sith, when that’s not the case. (Also worth noting that in the Zahn books before the prequels, it’s established that Yoda and Obi Wan could have wiped the floor with Vader and the Emperor if they wanted to, but they chose not to, both to avoid abusing their power and to give Luke and the rebellion the real victory.)
You can say oh well, that book is obsolete because the prequels superseded it, or because it’s from the old EU and not the Disney canon (for me it supersedes both,) or because you just don’t like it. Whatever the case, the point is that this was the understanding that people had before the prequels or other material came in, just going off of what is actually shown and said in Return of the Jedi.