I would suggest to you the advantage, at present, of being very sparing in introducing theory in your papers (I formerly erred much in Geology in that way): let theory guide your observations, but till your reputation is well established be sparing in publishing theory. It makes persons doubt your observations. How rarely R. Brown ever indulged in theory: too seldom perhaps! Do not work too hard, and do not be discouraged because your work is not appreciated by the majority.

Letter to John Scott, quoted in More Letters of Charles Darwin: A Record of His Work in a Series of Hitherto Unpublished Letters, volume 2, page 323 (1903)