No Buzzword AOP

I believe many people are interested in some AOP articles that frequently appear in the garden recently.
However, from the comments in the article, we can see that some friends still do not know the so-called AOP, and may wish to see more simple and vivid introductions to the various terms in the article. Next, I will try to use the simplest language to talk about my small understanding of Aop. You don't need to know much about object-oriented, but do not need to know the so-called design patterns.

Why do we need functions (structured programming )? --- To eliminate duplicates
Why do we need classes (Object-Oriented )? --- To eliminate duplicates
Why do we need aspect (Aspect-Oriented )? ---???

No Buzzword AOP --- when we don't have aop
No Buzzword AOP --- with AOP (Method interceptor)