Ah, now I understand. For a germinating seed, you should water just enough to keep the soil moist, not muggy. As a plant grows, it's roots will spread wide and deep to get access to more and more soil, and thus the moisture retained in the soil. So the larger the plant, the more water supplyes become available to it. For this reason, you need to water only if it hasn't rained for a long time and there're still no clouds in the sky. Many would argue with this, but if you water a plant that's soil already has a good amount of water the excess will only drain lower in the earth. By the way, it is healthy for a plant to have the top layer of soil dryed from time to time: this way, the upper roots can take up oxigen while the lower roots still get the plant some moisture.