Living defensively may be good for one's chance of survival but is not that glamorous to tell. That should, as you correctly pointed out, be taken into account. What happens now when one's fear is ending up without having a life to talk about or not living fast enough? Joke aside, I think that, besides a fringe minority whose choices are dictated by kicks and thus subject itself to the high risk of natural (de)selection effect, most of us have lifes dictated by the self preservation instinct.