Our brains are difference engines. We are especially attuned to notice changes. In music, it's common practice to make sounds quieter and less robust right before a "drop" where the song then sounds even more full just by adding those normal frequencies back into the spectrum. It's the difference that creates that feeling of explosion and energy. I find it insightful to notice how often this principle shows itself throughout life, and how it can be exploited against me. For example, if I simply spend some spare time in silence or meditation, I often find that right after, I'm more willing to take on mundane tasks than if I had spent that time before scrolling social media or even just blasting music. The boredom of silence and nothingness through meditation has reset the contrast meter in my brain to see almost anything else as a more pleasurable and enjoyable experience. Yet, if I spend those extra moments filling myself with numbing instant pleasures, like scrolling through social media or even listening to my favorite tunes, my brain starts to find added friction when thinking about reverting back to the more mundane tasks I have to go back to. My pleasure meter has reset to a higher level (the social media scrolling), and now the contrast to go back to work is a negative distance. Neuroscientist Andrew Huberman explores this at a neruochemcial level in his research, which I find to be endlessly fascinating and have not fully come to an understanding of by any means.
This idea even makes me think about the concept of "happiness." In a way, happiness can never be a permanent destination. Happiness only exists if it can be put in contrast with respect to something else in your life. If you have happy days, then by definition you must have days when you were less happy. If you have a sad day, it's because you've had days before it that were not as sad. Otherwise you wouldn't need the adjective to describe them — they'd just be days. This, to me, actually sounds quite beautiful. There is meaning because of the peaks and valleys — otherwise it all would just be the same. And in any valley, there will always be a peak around the corner, because there has to be.
Ultimately, it seems if you can ascribe pleasure to the journey, and not to the destinations of being happy or sad, you just might be able to tap into an infinite contentment — because those other destinations don't actually exist.