One part of Buddhism (mainly Zen Buddhism) is the concept and use of "Mu" (Wu in Chinese) which means nothing, or nothingness. This is a big aspect in Zen. One reason is that if we detatch ourselves from wordly posessions then we also must let go part of that mind that is attached to them. This is before-thinking mind. When we return to before-thinking, we return to Mu.
A monk once asked Zen Master Joju, "Does a dog have Buddha-nature?" Zen Master Joju turned to him and shouted, "Mu!" (which means no). The monk was confused because the Buddha had taught that every living thing had Buddha-nature but here was this great Zen Master telling him that a dog didn't have Buddha-nature!
There is a reason that Zen Master Joju said "Mu" to the monk. The monk was thinking too hard, he was attached to Buddha-nature. Joju used "Mu" as a sword to cut through the monks thinking. When he said "Mu," this cut off all the monks thinking, he returned to before thinking. This is also known as don't know or don't know mind.
In this state of mind, there are no opposites. No heaven, no hell, no light, no darkness, no happy, no sad. Everything just is what it is, no more, no less. This is a hard aspect for some people to grasp. If someone you love dies, you grieve, and you suffer. But why do you suffer? Because you want them to be alive again, you don't want them to be away from you. This is wanting. They have already proceeded from life, you cannot bring them back, you cannot change the situation, and if you choose to see the situation as it really is, and understand that perhaps it was merely all an illusion to begin with, comfort will come. If instead you choose to cling tightly to the fact that it makes you unhappy, you will be unhappy. By the usage of your mind, you can shape your reality, by attempting to be detached, you can save yourself from pain and suffering.
From this, detach from all things, get enlightenment, and save all beings.
-Buddha_in_Training
