The statement "anything that goes up must come down" is a generalization of the effects of gravity on objects. In the case of rain or a cloud of rain, they do experience the force of gravity just like any other object.
Raindrops are formed when water vapor in the atmosphere condenses into liquid droplets. These droplets are relatively small and light, and as a result, they experience air resistance as they fall through the atmosphere. The presence of air resistance can cause raindrops to be carried along by air currents and to have a more complex path of descent compared to larger objects like a ball or a rock.
Clouds, on the other hand, are made up of tiny water droplets or ice crystals suspended in the air. While they may appear to be floating, they are actually subject to the force of gravity. Clouds are formed when warm air rises and cools, causing the water vapor in the air to condense into visible droplets or ice crystals. These tiny particles are very light and can remain suspended in the air because the upward force from air currents counteracts the downward force of gravity. However, this is not a negation of gravity but rather a balance between the two forces.
Eventually, raindrops become large enough that the force of gravity overcomes the resistance from air and they fall to the ground as precipitation. Similarly, clouds can release their moisture in the form of rain when the droplets or ice crystals become too heavy to remain suspended in the air.
So, while rain and clouds may appear to defy gravity or float in the sky, they are indeed influenced by gravity and will eventually come down due to the gravitational pull of the Earth.