In anything that does cover the whole of your life - in your philosophy and your religion - you must have mirth. If you do not have mirth you will certainly have madness.
I approach every part I'm asked to do and decide to do from exactly the same angle: who is this person, what does he want, how does he attempt to get it, and what happens to him when he doesn't get it, or if he does?
Murder in the murderer is no such ruinous thought as poets and romancers will have it; it does not unsettle him, or fright him from his ordinary notice of trifles; it is an act quite easy to be contemplated.
There are many definite methods, honest and dishonest, which make people rich; the only instinct I know of which does it is that instinct which theological Christianity crudely describes as the sin of avarice.