One of the reasons people might be fallible, why we might fail to do what we try to do isignorance, that we have a limited understanding of the laws of the world - the physical laws that govern the world and of all the particulars of the world upon which those laws work. And then there's ineptitude, meaning that the knowledge is available, but individuals fail to apply it correctly. The third source is "necessary fallibility." That is, we're never going to be omniscient, there is some knowledge that we will simply never achieve, and there are limits to what we will be able to do.