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.
I believe it's more of a spectrum.
That said, I think people should drop the notion that humans are rational. We're boundedly rational, and this is balanced with logical reasoning.
It's often said in pop culture/society that being rational is somehow "better" than being emotional. I used to believe this long ago, but now I think that's bull. Emotions exist for a perfectly valid purpose, as a guide to our environment and how to interact with and control it. The fact is many humans make decisions or process information on solely emotive rather than rational pretexts. As an example, two queues were open at the supermarket the other day. The first had a really obese woman serving but was far shorter. The second had a cute Indian woman serving, but was far longer. I took the longer queue, just to say hello/making chit-chat/flirt with the cute woman. To some this is "irrational", but to me it's emotive and instinctual. And generally this is how humans often behave in the real world, and there is nothing wrong in that.