The reasons are different.
I was asked the first today and answered as honestly as I briefly could that I became a Christian because I realized that if I believed in anything I had to believe in God.
(And, having believed in God, it seemed clear that the Christian concept of God was correct.)
But I realized this sounded rather as if I was saying that it made no sense for anybody not to believe in God - that belief was logically-entailed...
That can't be right, because that is not how it is supposed to work - and the fact that something seems incoherent does not mean it is certainly false.
Nonetheless, historically that was pretty much why I became a Christian - but I remained a Christian because I saw that there was enough evidence to make it plausible that Christianity was true; and that since Christianity could be true, then I decided that was what I wanted to believe: therefore that is what I chose to believe.
(I had to choose something; I had to choose one way or the other - that was my choice.)
And, having made this choice; some time later I was granted the conviction - the revelation - that God was real, Jesus Christ was real, and His Son - and all the rest of it.
So that was (in a sense) an end of it - no doubt, no need to doubt. No going round and round asking the same questions. Just the quest for clarification, for spiritual progress, for theosis. That being the hard thing, and the main purpose of mortal life.