Nils Bohr chose
Contraria Sunt Complementa
as motto for his coat of arms. According to his son and others, Bohr distinguished between the logical properties of trivialities on the one hand and profound truths on the other:
The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. [Unsourced]
There are two sorts of truth: Profound truths recognized by the fact that the opposite is also a profound truth, in contrast to trivialities where opposites are obviously absurd. [Quoted by Hans Bohr]
It is the hallmark of any deep truth that its negation is also a deep truth. [Quoted by Max Delbrück]