Dialectic is a pretty highfalutin word but when described in simple terms shows us a valuable lesson for how to operate in the world.
Dialectic describes a way of thinking.
The dialectical method consists of a thesis, antithesis and synthesis.
The Wikipedia entry on dialectic contains this description,
The dialectical method, is at base a discourse between two or more people holding different points of view about a subject but wishing to establish the truth through reasoned arguments.
Dialectic comprises three stages of development: first, a thesis or statement of an idea, which gives rise to a second step, a reaction or antithesis that contradicts or negates the thesis, and third, the synthesis, a statement through which the differences between the two points are resolved.
This description of the dialectical method is pretty dry. Let's say you are interested in finding an answer to the question - should people be allowed to smoke?
You could read some stuff from the tobacco industry and those with a libertarian bent, then read some stuff from doctors and other worry warts ;-) then decide what you think.
To know what "you" think you have to be open to examining both sides of the argument.
Here's another example using the "she said, he said, I said" idea...
She said immigrants are dangerous.
He said immigrants are valuable
I said - (whatever you think after doing your own research and considering both sides of the argument)
It all ties back to the idea that for a "you" to exist you have to know what you think - not just what someone else tells you to think.