In the definition, ε > 0, with δ > 0, let x satisfy 0.

Intuitively, the main contradiction between ε and δ is concentrated in the case that ε and δ are relatively small, but this point is not directly stated in the definition. Therefore, technically, it is necessary to consider the case that ε or δ may be relatively large. If we want to simplify them into relatively small cases, we must be bound by ourselves.

Restricting the range of ε or δ is equivalent to strengthening the conditions, so that you can or can easily draw strong conclusions, such as your problem here, at least -2.

Similarly, you can set it to 0.