If he weren't ambitious, then watching TV wouldn't be a waste of time. It would just be something he enjoys doing. The fact that he has some ambition is what causes him to feel guilty when he's not being productive. No ambition, no guilt.
^That is true. So I think the reality of OP's predicament is a little more subtle. It's probably "the desire to be/become ambitious" rather than overt, naked ambition. The two aren't mutually exclusive, too.
There are also some nice Zen-sounding arguments that you can't fully realize your ambitions until you relinquish your desire to be ambitious– because you suffer from all sorts of perfectionism and performance anxieties, etc. But it's possible to argue either way– talk is cheap, actions are the differentiator.
If he weren't ambitious, then watching TV wouldn't be a waste of time. It would just be something he enjoys doing. The fact that he has some ambition is what causes him to feel guilty when he's not being productive. No ambition, no guilt.