Perception is a big thing. What we perceive can be totally different from what is actually going on. Consider the following, which is a buddhist tale..

Suppose we are walking down the country road at night. We look down at the ground and suddenly we see a snake and become frightened. Then we turn our flashlight on it. We look again and we see that there is only a rope, no snake. The rope was there all along, never a snake, but the rope appeared to us to be a snake because our sight was obscured by the darkness, because we did not focus our light on it. As a result of seeing a snake we became filled with fear and worry. When we found that it was only a rope, the appearance of the snake dissolved. We can compare the snake to the idea of self or ego, the flashlight to wisdom.