That loud, boastful arrogance mistaken for confidence is usually just the opposite, a reaction formation where what is repressed is broadcast in equal and opposite force to the world. Boastful arrogance on the outside, doubt and insecurity on the inside.
Regardless of innate talent and the amount of work put in, doubt and insecurity are likely to arise at times. From the mindfulness perspective it makes a whole lot more sense to embrace these states of mind honestly rather than trying to cover them up with pompous grandiosity. They might point to important elements for a successful outcome that really are lacking, elements that will be overlooked if these states of mind are quickly repressed due to the discomfort they cause.
You might not be as far along as you would like, both in terms of talent acquired and progress made, but you can emulate those who are and what you’ll usually notice emanating from them is a quiet confidence, an imperturbable outlook where they don’t feel the need to be vocal about successes or failures because they know at the deeper level that they’ve got the goods.
This kind of quiet confidence might not be as flashy but it’s at the heart of equanimity, and equanimity gives you the calm focus you need to keep going in spite of setbacks. Loud confidence might bolster you in the moment but it’s too much energy expenditure in the long-term, too much disappointment and embarrassment when things don’t go your way. Better to go about achieving your goals with the firm belief that if you do the very best you can good things will eventually happen. It’s not necessary or useful to constantly proclaim this fact to the world.