Has there ever been a moment where you felt you were doing fine but in hindsight you were a lot more vulnerable/troubled/worse off than you thought?
Around 2 years ago, when I first made a reddit account, I spent a lot of time on AskReddit asking about 'why are women so hard to date' like a personification of the dunning-kruger effect (while I don't think I've really learned anything about dating and socialization since then, I have stopped thinking women don't share the same basic emotions and reactions as men and in general don't think they're so removed from guys). Given that and how little engagement my threads were getting (it's AskReddit, but I didn't know what I was expecting) I was basically ready to be made an incel. Thankfully someone snapped me out of it by calling 12-year old me a neckbeard, which terrified me away from touching dating for a few months at least.
PS: If the answer is "if you don't feel like this you're in trouble, people don't/shouldn't just stop developing like that", I won't be surprised.
Absolutely, such is life.
Every moment that you feel great, wonderful, fantastic, and/or at the very top of your game - time will go on and you will have more ups and downs past that moment of spontaneous courage and excitement.
As time progresses you will learn more, you will feel more, and you will be something of a slightly different person (especially after two years).
When you look back you will notice these tendencies and where they were right and just, or where they were wrong and worrisome. This is a positive thing, it means you can look back and appreciate those moments as well as view them critically.
Be proud that you can change and view past experiences critically through a new separate lens.
Regarding your story, OP, I wonder if the incel’s idea of an abstract woman is an intentional defense mechanism or just an easy false conclusion to come to. Surely there are plenty of insecure men that aren’t so separated from women that they can think of a gender in this monolithic way. Do incels intentionally construct what they think of as a “female” to shelter their insecurities? Or is there happenstantially an intersection of insecure and socially isolated men that will naturally come to such a conclusion?
It may be as simple as:
"Things aren't going the way I want. But I know the problem isn't with me, so who can I blame this on?"
I feel like that covers a wide swath of detrimental behavior. I know I myself have found myself in that mental trap many times over the years. Telling other people what they should do different is easy. Changing yourself is hard.
That sounds like growing out of adolescence to me. But it's not just adolescence - like @drannex mentioned, everyone's constantly growing. The more you learn about people unlike yourself, the more you will experience this feeling.