[Yoda tries to convince Luke not to leave]
Yoda: You must not go!
Luke: But Han and Leia will die if I don't.
[Obi-Wan's Force-spirit suddenly appears]
Obi-Wan: You don't know that. Even Yoda cannot see their fate.
Luke: But I can help them! I feel the Force!
Obi-Wan: But you cannot control it. This is a dangerous time for you, when you will be tempted by the Dark Side of the Force.