Wow. This thread really became derailed.
I’m not gonna touch the drama with a 50 ft pole. Not productive at all..
I understand where the OP is coming from, and I agree that the singular phrase “Just be more confident” is not very helpful. That’s like someone asking “How do I become rich?” And you respond “Make some money.” 
However, I disagree regarding the ‘two camps’. Good experiences can increase confidence. Bad experiences can lower your confidence. But here’s the thing missing point. How does that first good experience come along? By putting your ego and pride on the line and going for it. If you’re learning a new skill, you will fail several times before getting a good experience. No one picks up a new skill without some failure. At some point, risk is required, your ego must be wagered, and you will be uncertain about the outcome.
So, if good experiences definitively increase confidence, bad experiences decrease confidence, then it seems like the only way to really increase confidence is to survive the streak of bad experiences until the good experiences start rolling in. There comes a point where you decide that it doesn’t matter how many times you fail, you’ll keep trying. Otherwise, you would try something once, see that you failed and refuse to try it again since you’re looking to increase your confidence, not decrease it.
Positive thinking is the key then. If you don’t believe you can learn a new skill, why you would continue trying to learn it? Thus, if you are to succeed and learn a new skill, and which, hypothetically should lead to good experiences and consequently increased confidence, then you need to believe you can learn the new skill.
So we discover that success truly is a matter of belief. I have confidence, and if some people looked at me, they might assume confidence comes easily to me. I’m tall, I’m muscular, I’m smart, I’m handsome, I’ve got charm. But do you honestly think I haven’t failed before? Have I ever crashed and burned horribly? I sure have. Many many times. If I let those failures effect me, then I would never have gotten anywhere. But I didn’t. I learned what I needed to from the experience and have grown.
That is why the ‘mentalists’ assert that changing your mind is more important than experiences. You really do create your reality, but until you accept that belief, you will only see the limitations you create for yourself. I have a friend who is always having financial and emotional problems. He refuses to see that he is causing his own problems. He blames his past, and his disability. What I see is that he is lacking money because he doesn’t have a job, spends his money on cigarettes, non-nutritious microwavable food and other ways of spending money in the wrong places. He doesn’t look for a job, and instead complains about the kids who get support from his family. When it comes to his emotional problems, I see his instigating and causing his own problems, but then blaming his parents. He wonders why his landlords won’t give back his deposit when he trashes his apartment like he has a daily janitor. Essentially, he’s content being stuck in in his reality and refuses to accept that only he has the power to change his situation.
Sorry, I’m getting off track. Anyways, the point I was trying to make was that we do control our reality. The whole inner/outer locus on control thing. It’s just a matter of if and when you see this. If you deny this belief and you find what you’re looking for, then cool with me. But if you are still struggling later down the road, give it a try, you don’t have anything to lose by thinking positively.
Ultimately, Gegogi’s comments regarding confidence resonate the most with me. Confidence is definitely earned. How did I become confident? I took risks, when those risks burned me, I got back up and tried again. When I realized that I started succeeding, the confidence came. But again, it’s not because of the good experience that I became confident, it was because I overcame a challenge. I overcame my insecurities and went for it. I ignored the bad experiences (the critical ‘mental’ aspect), and embraced the good experiences.
In learning to play lacrosse, I dropped the ball several times, gave up countless goals, and was laid out onto my back until I was too sore to move. My confidence came when I began catching the ball, stopping plays, and laying out other people. I made team captain before any votes from my teammates were cast. I earned that captainship like I earned my confidence in my lacrosse abilities. Those good experiences weren’t just handed to me.
The mentalists aren’t bullshitting you, but I do think that they are jumping a little ahead of the point that you are at. That’s why you view it as two separate perspectives. Okay, I feel like I may be going in circles here. Just my thoughts, I need to go pick up some ganja real quick. 
, but that’s another word that starts with ‘C’.