Look at Buddhist scriptures. Why can a Taoist mage predict something?

Because they gained the ability of avatar through practice. In addition, their wisdom is very high, and they can predict some things through the calculation of causal laws. For example, if you eat expired food today, you will have diarrhea later. For example, if someone does something illegal, he will go to prison. For example, if you hurt others, you will be hurt by others in the future.