This concept (in Dutch it is complementaire tegenstrijdigheid of tegenstelling) is easy to understand. Positive and negative, high and low, black and white, empty and full, alive and dead, all these concepts can only exist when their opposite / contradiction also exists. As Laotse says (#2): being and non-being give birth to each other.
So, do not try to banish the evilness from this world, for you will lose the good as well. Do not try to banish sin from the world, if you want to hang on to mercy. It is as simple as that.
Therefore, accept the bad times in live as complementary to the good times. Accept another mans opposite opinion as complementary to yours. Accept hate and love as opposite poles of the same emotion.