It could have been years or months. But let's say we're doing the population of insects that reproduce quite quickly. So days seem like a nice time span to care about. Now, what would be a reasonable model? Well, we could say that the rate of change, the rate of change of our population with respect to time, with respect to time, is, well, a reasonable thing to say is that it's going to be proportional to the actual population. The actual population. Why is that reasonable?