Happiness is a broad term for a positive emotional state, but each of the layers contributes to it in their own way.
The external world typically provides instant, short term happiness from scrolling, games, junk food, partying etc. This is great for exceptions, but less applicable in normal productive life. The most sustainable way to use this is to have a small treat after a good amount of work has been done.
Your own internal activities and progress provide surface, medium term happiness, like feeling good at the end of a day because you got a lot done. This type of happiness is motivating, as it feels like tangible progress is being made in your activities.
Finally, when the core sees movement in the correct direction over time, it provides deep, long term happiness that sits in the background and improves general wellbeing. It’s easy to forget about this within the space of a day or week, but when you feel low, deep happiness is a great fallback to rely on.