If the Bible isn’t perfect, why believe any of it?

If, for instance, the Flood is hard to swallow (where did all that water come from? where did it all go?), then what about other miracles in the Bible? Why accept anything in contradiction to our modern understanding of how things work? Joshua’s horn, Jonah’s whale, creation of Earth, virgin birth, resurrection of Jesus, etc.? Where do you draw the line? And if the Bible was written by unreliable writers who at least sometimes presented stories as truth, why believe any of it? Some parts don’t seem impossible, but is that enough to call them true? If God didn’t make the Bible inerrant, can it be a source of certainty about Jesus? If not, what reason is there to be a Christian?