Feelings
Feelings are the evaluative dashboard of our primal core.
Feeling good = all is well. / Feeling bad = need to change something.
This is so obvious as to be uninteresting, but it has profound implications. On one hand, our culture has been built on a foundation that prioritizes rationality (e.g. observable, tangible, measurable) over the emotional for good reasons. Our emotions are so responsive to simple inputs (e.g. sleep, food, chemicals like alcohol and caffeine, etc.) that trusting the conclusions they provide has been the very definition of irrational for millennia.
Clear as that may be, the limitations of emotions are only half the story, and there is another dimension of the truth we also need to respect. Feelings emanate from our unconscious primal core, and thus are important and useful indicators for primal-level relevance. If I feel like a failure then I am experiencing failure--and it makes no difference if some theory or other people say that I’m actually successful. I have known many people that I consider successful, but it’s rare to find a successful person who actually feels successful. Childhood food preferences provide another great example: I had a visceral hatred of squash, and knowing that hungry kids in Africa would be grateful for it was utterly irrelevant--eating my required bites still made me gag. While rationality would have us ignore our emotions, wisdom respects the primal feedback they provide.