Tyger! Tyger! explores the Beauty and Cruelty of the tiger as a perfect symmetry.
In The Marriage of Heaven and Hell, he says:
Without contraries is no progression. Attraction and repulsion, reason and energy, love and hate, are necessary to human existence.
I think these abstract concepts have huge practical implications. They tell us not to be overly concerned with a single polarity. In any case, polarities have great difficulty in surviving on their own: cut a magnet in half and see what happens.
I had a salutary reminder of this the other day when a workshop I was facilitating got into choppy waters. Frustration and resentment against senior management, who were not present, built to fever pitch. I felt an urge to move on to more 'productive' territory where we'd started (the other polarity), but experience told me to embrace the sentiment in the room. We even got to the point where I invited the most disenchanted to leave if they thought that further debate was pointless. I should point out I put this to them in a constructive and positive way, with no edge or animosity.
At the end of the meeting the group resolved to make a formal representation to management and disclose everything that had been discussed. But the big win was that they all declared, to a man, that they now felt themselves to be a team, understood one another and were united in their common objectives. Not bad for a team comprising several different contractors and a council with a track record of poor collaboration.