A thermometer is a device used to measure temperature.
An thermostat is an instrument which directly or indirectly controls temperature.
All persons reflect either a thermometer or a thermostat in life. Just like a thermometer merely reflects the temperature around it, some just reflect persons around them. These persons are followers.
Other persons, like thermostats, control their surroundings. These leaders influence others in all they do.
Are you a thermometer or a thermostat?