Quote from Rabbi Yehoshua Alt on Torah.org:
A famous Baal Teshuva related how he became religious. He said that he was once traveling to America from Israel and forgot to bring books to occupy himself on the flight. That left him with his thoughts on an 11-hour flight. It was in these 11 hours that he realized that Hashem is reality and decided to begin to live his life according to His will.
(I don’t know who the story is about.)