My inspiration came from my own experience with plants that I couldn't water (I usually put too much water and they die). So I started researching how ”professional” gardeners keep their plants hydrated and alive at the same time on the internet.
Drip irrigations, for example, keep plants with the proper quantity of ground moisture, as I discovered. So I came up with the notion of calculating the percentage of water in the earth. That way, I'd never be able to kill plants again.