When describing basic actions at the present moment, you need to think in terms of stative and dynamic verbs. My rule-of-thumb is, if you can draw a picture of it physically happening, then the verb is dynamic. You really need to follow this closely to have a proper grounding in English grammar. The so-called "exception" is a more advanced use and focuses on the immediacy or temporary nature of the action. Believe me, you'll find more.

English is full of exceptions to the rule. "Enjoy" is a stative verb of emotion. However, unlike most stative verbs, it can be used in the continuous sense. Some verbs can be both stative or actions, depending on how they are used. (see http://www.eclecticenglish.com/grammar/PresentContinuous1H.html and http://learnenglish.britishcouncil.org/en/grammar-reference/stative-verbs) "I'm enjoying this cake. It's so tasty." Is fine. It emphasizes that right now you are eating the cake. For: "I enjoy this cake. It's so tasty." Is OK, but most commonly, we'd say, "I like this cake. It's so tasty." We could also say, more generally, "I enjoy cake. It's tasty."

There are some verbs which can be used as stative as well as dynamic. I guess "enjoy" is one of them. If you say " I am enjoying this cake " you are talking about this specific time only. ( dynamic ) if you say " I enjoy this cake " it means you like this cake and you enjoy it each time you eat it. (stative ) Another example: If I say " you are nice " it means the quality of being nice is part of your personality. But if I say " you are being nice " it means you are behaving nice this time not usually.