Bottom logic refers to the method of thinking that starts from the bottom, the essence of things, to find the path to solve problems. The stronger the underlying logic, the stronger the ability to solve problems.
The meaning of "the user you called is busy" may be: 1) the other party is talking to someone else; 2) after a few rings, you hear "the user you called is busy", which means that the other party hangs up your phone; 3) the other party may have blacklisted you; 4) the other party has blacklisted you; 5) the other party has blacklisted you; 6) the other party has blacklisted you; 7) the other party has blacklisted you.