Not to rag on humanity or anything (okay, maybe a little bit), but if people could be a little more like the animal characters in Mrs. Frisby and the Rats of NIMH, there might be more good news every day in the morning paper. It's not so much that the characters here are nice all the time, because who wants to read about that all day long? It's that they have a strong moral code, which says that if someone has made a sacrifice for you, it is your responsibility to pay them back with a sacrifice of your own. That's also how the plot moves along, too. Mrs. Frisby helps Jeremy; Jeremy helps Mrs. Frisby. Because Jonathan Frisby helped the rats, the rats will help his family. And so on and so forth in a long chain of furry animal goodwill that is downright heartwarming when you really think about it.
These characters are always making sacrifices for each other and sometimes it feels kind of unrealistic that they would do so much for someone else.
The only way that the characters can survive in this dog-eat-dog (or cat-eat-mouse) world is through a willingness to sacrifice him or herself for the greater good.