In your opinion what causes christians to believe in Jesus

[Alan V]

Just as advertisers wouldn't use their techniques unless they worked a certain percentage of the time, neither would religious people (all else being equal).

That's not to say religious people can't lose ground over time because of such factors as child-abusing Catholic priests, money-grubbing protestant ministers, terrorist Muslims, and, I am glad to say, the proliferation of atheistic arguments online and elsewhere.