The theory states that I will find myself surviving indefinitely because there are infinitely many my copies in the infinite universe, and some of these copies will not die in any risky situation. The theory is called "quantum immortality" because it is based on many worlds interpretation of quantum mechanics. Though, in this question we doesn't insist on validity of MWI. There could be other mechanisms which create many my copies, like chaotic inflation. The question is related only to observable consequence of quantum immortality: that I will always find myself alive.