The deepest questions that engage our minds are not easily answered and to gain any real insight into them one has to make a considerable effort. Philosophy is a hard subject. Some of the greatest philosophers have also had outstanding gifts for lucid exposition but even they, even Plato, Hume and Russell, are heavy going. If it is useless for philosophers to write only for philosophers it is equally unprofitable for a non-philosopher to take up a serious philosophical work without being prepared to invest much concentration in reading it.
(William Charlton, The Analytic Ambition: An Introduction to Philosophy [Cambridge, MA: Basil Blackwell, 1991], 2)