Appreciating art vs appreciating people.
We appreciate art. In order, one could be apt to appreciate art he needs to learn understanding art, its nuances, history, the unknown language of forms and tones. Not everyone wishes, can or should step on this path of engaging in such an effort. Should he chooses not to - he still can have an affinity toward an art piece, he can casually or even with a serious tone of voice say “I like it”.
The very same could be said about our relationship with another person. If we are not (pro)actively and consciously engaging with others with an intent to learn to understand - we will never be able to truly appreciate a man. We still can say “I like him or her” but we deprive ourselves of one of the most rewarding feelings - appreciation of and gratitude to another human being.
Yet as in the case with art - we have to put an effort. The effort of learning how to appreciate others (not in a generic way referring to the whole humankind, a massive of given civilization), but those concrete people you have or you would like to have a close relationship with like your partner, family member, or friend.
If art analogy hasn’t enough to build a convincing argument - I will let the Harvard Happiness Study do its justice (just search in a browser).