TLDR: I'm honestly not sure how to summarize this because the set of feelings I'm describing might be pretty unique to me? This is also pretty personal so it's outside my usual realm of tech-centric things. I mostly wrote it for myself as part of a committment to more writing and other people in the same headspace.
Here's a seeming truism that is going to strike most people as extremely obvious: "other people are happy." Yet for a particular type of person (a person who has probably always been somewhat depressed), this statement is just sort of hard to fully believe. I say this because I used to be skeptical of this statement: I did not enjoy almost any aspect of my life and I kind of assumed that everyone felt similarly. Being happy was a shared fiction we all agreed to pretend existed. We were all trudging through a mostly gray life, waking up and struggling to convince ourselves to begin the day. That this is not the case has been one of the most powerful revelations of my life: some people are genuinely having fun and actively look forward to most of their days. With every next thing they have to do they don't think "ugh, okay, another thing. Let me summon the energy to do it." Nope, they are actively looking forward to that next thing and the one after and the one after that.
Writing it now feels ridiculous and hard to convey how suspicious I was that anyone was happy. Obviously some people enjoy all or most of their life! If I could have tuned into someone else's head and realized the range of possible experiences, I would immediately have identified that something was wrong and gone to fix it. Instead, I continued trudging along. This is one of the tragedies of living in the world before computational neuroscience advances and we figure out how to experience other people's mental states; everyone is always just guessing at what it's like to be someone else.
I suspect one thing that made this harder is that for most of my life (I won't tell you exactly how long) I've been doing performative happiness. I was unhappy, acting as though I was happy, and therefore found it easy to believe that others were doing the same. Now look, obviously people would say things like "I'm happy" or characters in literature would be portrayed as happy but I felt that this was just Americans doing performative happiness out of some cultural requirement to never show weakness. For me the thing that kind of knocked me out of this skepticism was spending a lot of time with my wife who is just a deeply joyful person. In one way or another I'd kind of repeatedly ask her "are you actually happy?" and after hearing it enough times I just sort of started to internalize the belief that it was true since it would be a weird thing to lie about. Spending time with her is the closest I've come to being inside the head of someone else and I can see that it's just totally different to be her than it is to be me. So, over time it has become easier and easier to believe that other people are happy and that I have solid proof of it.
It is possible that the feelings I'm raising here apply exclusively to myself and not to a single other person in which case, well, that's surprising. However, it feels unlikely that I'm unique here and I desperately hope that if someone shares the feelings described here then I can spur them into action. I suspect most people fall along this spectrum, being unhappy for a good portion of the day, but it doesn't have to be this way! Find a therapist! Start meditating! Spend time with your friends! Do anything and everything you can to find a way towards genuine enjoyment for the majority of your time. It'll be a process but it's worth trying to believe that it's possible.
Again, I want to stress that this all sounds like a silly truism but the shift from disbelief to belief represents a profound internal mental shift for me. Now, you may wonder, are you a person who is at risk for internally believing happiness is a myth? Look deep and check if you suffer from the following risk factors:
P.S. As always, I should add that this essay comes from a position of privilege. Some folks lives are just hard by virtue of circumstance and I would feel ridiculous trying to argue that they should assume it's possible for them to be happy. I mean, it might be! I just don't know and I don't want to make claims about it.