Jesus... First of all, Yoda wasn't bested by the Sidious, he fled after he almost defeated Sidious because he ran out of time. They went into hiding because they knew they were no match for the entire Galactic Republic. The jedi were thought of as traitors and they were to be killed on sight. The only way to preserve the jedi was to go into hiding and protect Anakin's children who would undoubtedly be force sensitive. Obi-wan couldn't train him in the force for **** loads of reasons. His connection to his father, he would have to be trained while living with his family which was forbidden (attachments). Finally, the reason he didn't kill Vader was because he couldn't bring himself to. He couldn't in the third, even after he cut off his arms and legs lol, he didnt finish him. Also he knew there was still light in Vader, but knew that he wasn't capable of bringing him back. But he knew that Luke could. **** the notion that Yoda and Obi-wan, two of the most powerful force users in history were cowards, **** it.