First of all, the limit is the value of y when the function moves in a certain direction, and one x can only correspond to one y.

Secondly, if there are two limit values in the same direction or at a certain point, then this limit value does not exist.

You can see the above picture, and the positive and negative limits are not equal. But infinity can be divided into positive infinity and negative infinity, which are discussed in two directions. It can only be said that the limit of positive infinity is 1, and the limit of negative infinity is-1. Only when these two values are equal can we say that the limit is the same number when it approaches infinity. In fact, at this time, we still occupy the limit of two directions, but the limit values are equal.