Stay intellectually humble. It's a huge component of wisdom in my observation. Understand you can always make mistakes that can be corrected, and that you have arrived at your opinions through limited information that can always be supplemented, so stay open to both of these possibilities.

You can be confident in your opinions that you arrived upon through spending a lot of effort thinking about them, and you don't need to have self doubt when challenged on them baselessly. But when someone does point out an error or something you missed, it's essential you haven't become closed to accepting it.

Always remember what the basis are for your opinions and how well-founded they really are. For example: how much do you actually know about a thing when you're relying on something you read in the news? How much do they really know about that thing?

As a check on yourself believing you've put a lot of effort into thinking about something, be on the guard for unwarranted confidence. If a professional has put their efforts into something in their field of expertise they've spent their whole lives working on, chances are you haven't thought of something they haven't in the first five minutes of hearing about their work. That might seem ridiculous, but you see this all the time on Lemmy, where for example commenters seem to think they've figured out key errors in scientific papers after reading a single popular science article about an experiment or figured out solutions to incredibly complex problems like fair taxation.

Imo, you don't. You must remain humble and open-minded.

Simply keep saying "Fuck it we ball" untill you can ball no more

OP: I'm struggling with mental unwellness how do I deal with this?

Every reply: You know you should feel even more unsure of yourself, you're literally wrong about everything and you're also probably really dumb.

I hope that someone else in the room will challenge me.

I doubt literally everything and don't trust my own judgment. I'll thank my ex's affair for part of that.

By not being sure of myself on anything except subjects about which I have done a great deal of research and reading and/or have considerable personal experience and knowledge. This means that I am not "sure of myself" very much, and when I am, I feel justified in doing so

There's a line in Nicholas Roeg's movie Insignificance that has stayed with me for decades now.

There's an obvious Einstein expy just called "The Professor." At one point, he's asked why he's so cautious about his claims - why he habitually says things like, "I think that..." or "The theory is that..." or "One might argue that..."

His response is, "If I say 'I know,' I stop thinking."

That, IMO, points to the primary answer to your question - don't try to remove self-doubt. Nourish it. Revel in it. Because it's the thing that will keep you thinking, and the more you think, the more likely you are to get to actual truth.

You really don't maybe you shouldn't. I just try to compare new things to things I have done in the past and evaluate how much effort more it will take. At work for example: every change is 2 days. You want the little light to be green instead of red? 2 days. You want to change the programming language? Still two days. On average it works out. You just keep stacking successes behind you gradually taking on bigger and bigger tasks. Each one is only slightly harder than what you have already done.

It's important to look at the reactions you get. If what you're saying provokes discomfort or hostility, that's the time to reëxamine what you just said.

And further, when someone disagrees, try to politely ask why. Most people are willing to explain where you fucked up a long as you don't get defensive.

When the self-doubt is overwhelming, a gambler's desperate bet is made, to go all in hoping for a miracle.

When forced by circumstances, whether as a hero or a villain, one becomes the protagonist of an epic that foretells the rise or fall of an entire world.

When everything else fits perfectly into place, being right is the only truth worth considering.

It's always good to have self doubt, it leaves you open to changing your mind. Do what you think you should, but those who realise they are fallible will more easily change their view of things when proven why they should.

Find a friend who you can trust to be honest with you to second guess yourself with—preferably someone with a lot of emotional intelligence and self-awareness.