Common misunderstanding that dialectic means both sides come to the same conclusion. Most likely comes from taking too literally the symbolic language, or visual representations thereof, of thesis-antithesis-synthesis. It's not one side says something, thesis, the other counters, antithesis, and then you agree on a unified idea, synthesis. It's a never ending process. One side presents an idea, thesis. The opponent presents a counterargument, antithesis. Then the first side makes a counterargument to this, this is the synthesis. Then the opponent makes a counterargument again. Any given argument is any of these three, and all three at the same time, thesis-antithesis-synthesis. It's all relative, it all depends on what you relate it to. The first statement can only be thesis. But the second statement is antithesis to the first statement, the preceding statement, and simultaneously a new thesis, relative to the subsequent statement. The third statement is any of the three, thesis relative to the statement coming after, antithesis relative to the statement which came before, synthesis relative to the two preceding statements. It's a zigzag pattern, like a pingpong match.
A
--->B
A<---
--->B
A<--
...
This can also be shown as
A--->B--->A--->B--->A...
In this never ending chain you can take any one point A and it will have a B preceding it and a B following it, and you can take any one point B and it will have an A preceding it and an A following it. Any point in the chain is thesis to the point following it, antithesis to the point preceding it, and synthesis of the two points preceding it.