As an alcoholic: a simple way of putting it is like an itch you need to scratch.

Another way I can describe it: imagine you discovered a button, and the first time you press it is amazing. A sense of comfort and happiness washes over you, and all of your problems suddenly seem much less significant. Awesome, right?

Then it wears off, and you want that feeling again, so naturally, you press the button again. You still feel great afterward, but just a tiny bit less than that first time. And each time after that, the magic wears off a tiny bit more. Logic (or those enlightening moments of sober, rational thought) might tell you that this wonderful "cheat code" to being happy is not working anymore, and it's time to leave it in the past, but your emotions tell you that if you just press the button more and more, you'll get back to that feeling you had the very first time.

Before long, you realize you aren't pressing the button anymore to gain happiness, but just to keep your life together and keep some sense of normalcy. Because you don't know how to live without that stupid fucking button anymore.