What I have learned in reading and writing history of physics

After a fifteen year end-of-career excursion into reading and writing in the history of physics, I will give a personal talk about what I have learned, both the good and the bad. Historians do have a problem, to give an account of history (to quote Leopold von Ranke) ``how it actually has been.'' Sometimes we don't and can't know what actually happened in which case it is admissible and tempting to speculate. It is not all right to assert that such and such must have happened. The worst offense, in my opinion, is for authors to tailor their work so as to ``prove'' a pre-conceived thesis. Names will be named.