@alex717,
Further examples:
1. You and I are walking in the desert on a hot day. We see a lake shimmering at a distance and walk towards it. Sometime later, you turn to me and say, "well, it was a mirage after all, in reality there was no lake."
2. Using a magic carpet, we leave the desert and walk along a path. In the distance is a stone tower on the hill. You say, "look at that round tower over there" and point to it. The path takes us closer, almost to the bottom of the tower, and we find that, in reality, it is actually a square tower.
3. There is a large tree across the street in your neighbor's yard. In the summer it appears leafy and green; in the winter, the leaves are gone and only the stark structure of its branches are to be seen. In reality, though it is the same tree.