“Balance every thought with its opposition because the marriage of them is the destruction of illusion”
— Aleister Crowley
Neils Bohr said the opposite of a fact is a falsehood but the opposite of a profound truth is another profound truth. R Buckminster Fuller said that the universe can only be apprehended asynchronously. In other words there is no way that we can understand the complete universe at any one time. Therefore at any given time we can only have a partial understanding of the truth. How then do we go about getting closer to the truth. The way that Aleister Crowley suggests above is a good one.
Testing what we think and believe with their opposite is extremely useful tho for some people challenging. Many of us identify so strongly with our thoughts and beliefs that when they are challenged by someone, we take it as being a challenge to our very being itself. Instead we should welcome it and yes, challenge ourselves. If we are correct, than the opposing view will obviously fall apart. If we are mistaken than the opposite thought will enlighten us. Far more often tho, the truth lies somewhere in between and it is by synthesizing the two that we can reach a higher understanding. Of course than occurring to Hegel, we should then look at the opposite of our synthesized view and keep on going until we reach a total breakthrough beyond thought.
Blessings, G
Sky Dragon (Redux) by G A Rosenberg 
Hanging Out in the Garden Again by G A Rosenberg 