What is the main reason for the burning of micro reduction motors?

The main reason for the burning of micro reduction motors:
The main reason is that the micro reduction motors are not regularly maintained and serviced, the motors run abnormally, causing the temperature to rise, and finally the reduction motors are burned out. So what problems will cause the reduction motor temperature to rise?
1. The ambient temperature is too high.
2. The motor is overloaded and the temperature rises.
3. The motor is stuck, causing the current to increase and the temperature to rise.
4. The motor bearings are short of oil. The friction temperature is high, causing the temperature to rise.
5. The insulation of the motor rotor or stator coil is aging and the temperature rises.