Owl: A thermos of soup sits on a lab bench. Its temperature T(t) falls toward room temperature R. What should dT/dt depend on?
A sensible first model: cooling is faster when the soup is much hotter than the room, slower when the gap shrinks — so dT/dt = −k(T − R) for some positive k. That's Newton's law of cooling as a rate equation.
Models are maps, not the territory. They need units that make sense, parameters you can interpret, and initial conditions before you predict a future temperature.
If you ignore the initial temperature, what goes wrong when you try to forecast T(20 minutes)?