Happiness and expectations go hand in hand. This may help explain why women initiate divorces far more frequently than men (up to 90%) due to their expectations compared to men who think that everything is fine if the house isn't on fire. I wrote my own article about this:

https://franklinwuhoo.medium.com/the-bill-and-melinda-gates-divorce-just-another-in-the-flood-of-divorce-initiated-by-women-b02cd4ceca03

Expectations are definitely something entirely in your own mind and it directly correlates to your happiness. Unrealistic expectations = unhappiness.