There are two sides to everything, there is Positive energy and Negative energy, such is a fact and Qi follows the same path.
If you've never experienced it and you get the chance, it's quite a learning experience, there are some interesting characteristics of negative energy compared to positive, it seeks to use, destroy, crumble, waste where positive energy seeks to harmonize, build, maintain, unify and as such keeps together while negative doesn't, positive works together to maintain it's prescence while negative works solely to achieve it's purpose, thus positive will overcome.

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Oh THAT'S how that works!