Because I'm worrying much less about whether or not my work is good enough. It might be, and it might not be. It's just not worth the energy it takes to worry about it - especially when I could be putting that energy into the work.
If you're your biggest critic then nobody else can harm you. Your opinion of you means more to you than their opinion of you, so how could they harm you? Their words are just noise - sometimes distracting, but never compelling.
I subscribe to a "yes" philosophy, by which I mean I try to say yes as much and as widely as possible. Yes to spending more time doing the things I love with the people I love, yes to trying new things, yes to pushing my limits and taking on new challenges.
It is possible to measure the length of telomeres in routine practice from blood samples. There are several ways to lengthen telomeres that have been reported in humans that may be of benefit for heart attack prevention.