"The ethical rule is from Samuel Johnson who believed that maintenance of easily removable ignorance by a responsible office holder was treacherous malfeasance in meeting moral obligation. The prudential rule is that underlying the old Warner & Swasey advertisement for machine tools: "The man who needs a new machine tool, and hasn't bought it, is already paying for it". The Warner & Swasey rule also applies, I believe, to thinking tools. If you don't have the right thinking tools, you, and the people you seek to help, are already suffering from your easily removable ignorance."