"Unshakable confidence" means having a strong belief in oneself or something, regardless of any doubts, obstacles, or challenges that may arise. Full definition
He exercises regularly, pays attention to his personal appearance, and approaches women at the club or on a dating app with an aura of unshakable confidence. (datingadvice.com)
The limitless possibilities of cruelty are visible in his eyes, as he speaks untruths with unshakable confidence, delivering each line as if it's a dramatic reading of one of President Trump's tweets. (sfchronicle.com)
Along with all that training comes unshakable confidence. (entrepreneur.com)