Serious question: Why aren't Christians more trusting than they are?

I have a sort of code I live by, which is basically that I would rather be killed than live in a world where I am afraid to help someone in need. So far, it hasn't killed me in nearly 5 decades. Like today, I picked up a stranger that was walking down the Interstate between St Louis and Memphis with a gas can... he had walked about 3 miles of the 5 miles to the next exit without an offer of help. I'm not trying to say it makes me better, or Christians worse, it's just an example. I know a lot of Christians would be afraid to stop, and I guess that might be reasonable, but shouldn't trust in Jesus and willingness to help a fellow human in need override that fear a little more often than it seems to do? As a Christian, how do you usually justify passing them by?