A proclivity is a natural tendency to like something, such as your sister's proclivity for restaurants that serve hot, spicy food.
When you have a proclivity, it feels automatic — you like what you like; you don't even have to think about it. The origin of the word proclivity supports this feeling. Proclivity comes from the Latin word proclivis, which literally means "sloping forward." You slide toward a proclivity — no effort is needed. You just give in to it, since you're headed in that direction naturally.