Well, when you're absolutely certain you have nothing left to look forward to but inevitable slow decline and death, and hopefully without leaving the smallest trace of your blighted existence on the earth, mid-life comes along at about 33-35, and even the smallest of things, (like finding something in which to believe,) seem huge and crazy.
I remember two years ago, I wrote down my life's goal, "to get to the point of death without doing any damage to others on the way, to go away somewhere and die hidden and quietly, like an old cat might." Then, the mistake that was my existence could be quietly rectified. I would take nothing of life, because I had nothing to give, and I would feel ashamed for the air and food my body had wasted.
Then out of the sky one day came the mockingbird, who said, "ok loser, if you don't want it, I'll gladly step in and take it."
I gave it to her, and now I am her. Of course, she waited until I was totally committed to non-existence before she revealed that she was me all long.