Mendo, the know-how and method of doing things. Layman, a person who has no knowledge or experience of a certain thing or work. The insider, refers to the person who has rich knowledge and experience of a certain thing or work.

The meaning is: the insiders look at things to see the method to see the essence, the outsiders can only look at things to see the appearance, look at the hustle and bustle.

This performance is also explained in psychology:

Perception is the reflection of the human brain on the whole of the objective things that act directly on the sense organs. In the same time, the role of the human stimulus a lot, but due to the limitations of the information channel, people can not be clear reflection of all the stimuli, can only reflect those stimuli that are important to their own significance, this is the selectivity of perception. The stimulus that is clearly reflected is called the object of perception, and the one that is vaguely reflected is the perceptual background.

Therefore, for the "layman", the "buzz" is the object of perception, and the "doorway" is the perceptual background; while for the "insider For the "insider", it's the opposite.