What are the motifs in A Brief History of Time by Stephen Hawking?

Persistance is a recurring idea in the story. The discovery of a good overall theory of the universe may not be possible, yet Hawking and many others still persist in chasing that knowledge. The author has hope that such a theory will be discovered sometime soon, but so far this has not happened, or if it has, the theory is still too far down in the cauldron of theoretical physics to have percolated up to general scientific knowledge. Nobody can predict everything that happens with one theory, only bits and pieces here and there for specific purposes.