Here's why:

* Temperature is a measure of the average kinetic energy of the particles within an object. When two objects have the same temperature, their particles are moving at the same average speed.

* Heat transfer occurs when there is a temperature difference. Heat flows from a region of higher temperature to a region of lower temperature. This is because the faster-moving particles in the hotter object collide with the slower-moving particles in the cooler object, transferring energy and increasing the cooler object's temperature.

In summary: If two objects are at the same temperature, there is no temperature difference, meaning there is no heat flow between them. They are in thermal equilibrium.