The strict definition of (1) expectation is ∑Xi *π absolute convergence, and attention is absolute, that is, it is different from the commonly understood average. A random variable can have an average value or a median value, but its expected value does not necessarily exist.

(2)E(X)=5 does not mean that 5 will definitely appear, or it will appear the most times.

For example, there are two identical balls in the bag, one with 0 on it and the other with 10 on it. I hope to touch them once.

Obviously, the expectation of X is 5, but it is impossible to get 5.