When Obi-Wan looked to Luke in ANH, I don't think he saw the future as such, but he saw hope for the future, and realised what he could do to nurture this if he let himself go. So he sacrificed himself knowing he could not defeat Vader, nor would the others leave him behind. Remember, in ESB neither Ben nor Yoda could see the future, and both foresaw doom for Luke. Yet Luke essentially flew in their faces and left Dagobah untrained to face Vader. Luke forged his own path and made his own choices. Again in ROTJ, it was Luke alone who felt Vader's goodness, again proving Ben and Yoda wrong. In TPM, neither Qui-Gon, Obi-Wan nor the Council got it wrong. Anakin appeared to be the 'chosen one', a prophecy he ultimately fulfilled, Obi-Wan defeated a powerful Sith Lord in a battle which claimed his experienced master (graduation if you ask me) and Yoda sensed danger in the boy's future. He didn't think 'hey, this boy will turn and wipe us all out!' Remember, Anakin's full of goodness and becomes a great Jedi Knight. The fact is something terrible happens to Anakin, and the Council had become slow and procedure-ridden, and never saw the Sith menace coming. Obi-Wan blames himself, and is redeemed by his own guidance of Luke. Luke redeems everyone, and is a very strong character because he stands on the same threshold as his father, but does not fall. He also proves Mace Windu and the Code wrong...you're never to old. So back to the point, yes Obi-Wan's sadness is very poignant. He lives in exile and blames himself. But he is waiting, and knows the fight is not over. Consider Anakin's sadness. Aside from Eps II and III, and whatever happens between him and Amidala, Obi-Wan and his mom, here's a guy who you feel wants to destroy the Emperor, but is afraid. He wants his son, but wants him to destroy his master for him. He has twisted, perversly good intentions, is hungry for power and is crippled by fear. As a man, he is physically and emotionally destroyed. A man who once had everything. That's pretty sad.