So yeah.. all mammals do not avert painful situations and seek contented ones? If one kicks a dog, the dog actually likes that, or would not eventually fight against it? Isn't that part of the definition of sentience? Your point is essentially validating moving outside of one's comfort zone. However, I doubt many who advocate doing that would say humans don't by design seek situations of ease over situations of discomfort. Moving outside one's comfort zone via, say, learning to ride a bike is different from averting a stressful work or home environment.

As for non-mammals, well as humans are mammals, then I'm using our taxonomical order as a base. I don't know if the same applies to birds, reptiles or amphibians.