The One Main Teaching
The Lord Buddha told us He had only one main teaching and all of it concerns the cause of unhappiness and how to think and act in ways that will bring us freedom from unhappiness.
All living things want to be free from pain and other forms of unhappiness. Even little worms on the footpath feel pain and thus are unhappy if we step on them. There are many forms of life, some low, others high, but even the least developed living things seek happiness in their own ways. If we go to a river or a brook, we see that some fishes like to be close to the top of the water, near the sunlight. If something frightens them away from the surface and they have to go deeply into the darkness of the cold water, then they are unhappy and return to the upper, sunlit, warm water as soon as they feel it is safe. If the fishes that like the deep, dark, cold waters are frightened into the warm, upper waters, then they are unhappy because each of the many, many forms of life is seeking happiness in its own way.