For me it was just logic. Once I took the time to think about things we believed, I realized that it was ridiculous.
Then I realized my life was passing by, and since this is all there is, I'd better get on with enjoying it.
At the time there was a song by the Beautiful South, which marked me:
"I want my sundrenched Ingred Burgman kiss,
not in the next life,
I want it in this, I want it in this. "