I could say that the moon is an illusion, but this would be a gross falsehood. The moon does seem to exist, just as normality seems to exist for people. How to explain the differences in the perceived normalities?
Normal does exist just as the moon does, but the individual's experience of normal is like viewing the reflection of the moon in wind swept puddle of water. The reflection is a small reference of a larger reality, only a glimpse of the what is unseeable.