Faith
Jack O'Neill was never one for having faith.
He never had faith after his son Charlie died.
He never had faith when he and Sara got divorced.
He never had faith after his best friend Charles Kawalsky was taken over by a goa'uld and was killed by Teal'c.
His faith returned a little bit when he met Skaara but then that faith was taken from him when him and the Abydonians were killed.
But for as long as he lived he had to have some faith to know that the blonde Lieutenant Colonel / Doctor astrophysicist he loved would say yes to his proposal.
He just had to have a little faith.