I always thought that the best way to sum up my professional work is that it has been an almost equal mix of theory and practice. The theory I do gives me the vocabulary and the ways to do practical things that can make giant steps instead of small steps when I'm doing a practical problem. The practice I do makes me able to consider better and more robust theories, theories that are richer than if they're just purely inspired by other theories. There's this symbiotic relationship between those things. At least four times in my life when I was asked to give a kind of philosophical talk about the way I look at my professional work, the title was "Theory and Practice." My main message to the theorists is, Your life is only half there unless you also get nurtured by practical work.
-- Donald Knuth