[chousuke]

It's a bit difficult to disagree with "not everything", because that's obviously true; not everything even can be perfectly analyzed.

However, I think you can (and should) try to at least maintain awareness of your behaviour and its effects, but only because if you don't, you may actually end up acting in ways that contradict your values; or if your values are ill-defined or vague, you might end up not understanding what it is that really matters to you. I think rationality is a necessary part of having a well-defined value system, even if the axioms are arbitrary. "Letting people enjoy things that aren't harming anyone" is a rational decision based on my value system.

What I can use rationality for, really, is figuring out if there's something I'm doing that's actually in conflict with my own values, or if there's something I can do to nudge the world (or at least my own life) to have more of the things I value.