Haven't we all had those moments? We make a life-changing decision. It's well thought out, arrived at after extensive analysis and cogitation. We're very sure the right path has been chosen, and feel comfortable with our fully considered plans. And then the critical moment arrives, and the key and irrevocable first step is taken. All of a sudden we're beset with renewed doubts and fears. Can we step backward from this action that now seems so rash? What have we done?
I've certainly had such times in my own life. I remember quitting my job to start my own business, trading what at the time seemed to be a certain paycheck for the insecurity of having to generate my income by a swap of services for money. It meant that every day I had to return value for the fees I was paid, no longer could I rely on past performance to offset a "bad day." In a way that's a very rewarding challenge, but it's also a fearful one. I can also recall some other, similarly important personal decisions. Each time that initial move was dreadfully scary, prompting me to go back and again re-examine my premises no matter how thoroughly I may have already considered and evaluated every factor involved.
On another subject, the "survival-of-the-fittest" imperatives of human prehistory are well documented. One of the great luxuries that our social and technological development has afforded us is increased freedom from the consequences of natural selection. Today we can afford to override the choices that nature would impose on us, making the human decision to confer life where nature might have dictated death. It's one of the great rewards of social progress.