5. Obi-Wan Is Either Senile or Deranged
George Lucas kind of set himself up to fail with this one. When major characters meet or become aware of each other for the first time in a given series, you can’t just introduce them in prequels. There are two examples of this.
Obi-Wan should obviously have recognized at least Artoo if not Threepio. Besides the message for Leia, Artoo and Obi-Wan don’t know or need anything from the other that would have mattered.
The bigger example is when Obi-Wan doesn’t know about the other hope that Yoda mentions. Some people have introduced the argument that Yoda was referring to Anakin instead of Leia. That’s just an attempt to retroactively correct this. With all the references to Leia’s force-based family tree, the suggestion is that Leia might be able to master the force as well.
This is one of those times when the convenient sensory powers of the Force are ignored to add mystery or tension to the movies. Why does Obi-Wan not know information he should very obviously know?
Next: 4. That Death Star Weak Spot