Think black, white and gray
Penguin is a black and white thinker, making quick decisions that are usually "yes" or "no." Penguin thinks in extremes, so things may seem extra good or extra bad.
Donkey is a gray thinker, seeing more options that "yes" or "no." Donkey sees a whole middle area of possibilities. Sometimes, too many options make it difficult to make decisions. Donkey needs a lot of time to think.
Donkey and Penguin do not try to change each other's ways of thinking. They appreciate and help each other until their combined thinking makes everything work out.