Quote: Mental illness is questioning the point of living

Question

I'm trying to find a quote essentially relating the sentiment that "a mind which questions the point of continuing to live, is a mind which is mentally ill", as a definition of mental illness. I thought it was Freud, but I read three pages of quotes of him and didn't find what I was looking for. I found two that are close in meaning:

No other technique for the conduct of life attaches the individual so firmly to reality as laying emphasis on work; for his work at least gives him a secure place in a portion of reality, in the human community. The possibility it offers of displacing a large amount of libidinal components, whether narcissistic, aggressive or even erotic, on to professional work and on to the human relations connected with it lends it a value by no means second to what it enjoys as something indispensible to the preservation and justification of existence in society.

SIGMUND FREUD, Civilization and Its Discontents

“About a third of my cases are suffering from no clinically definable neurosis, but from the senselessness and emptiness of their lives. This can be defined as the general neurosis of our times.” ― C.G. Jung

Answer 1

In a letter to Marie Bonaparte, Freud wrote:

Im Moment, da man nach Sinn und Wert des Lebens fragt, ist man krank, denn beides gibt es ja in objektiver Weise nicht; man hat nur eingestanden, daß man einen Vorrat von unbefriedigender Libido hat, und irgend etwas anderes muß damit vorgefallen sein, eine Art Gärung, die zur Trauer und Depression führt. Großartig sind diese meine Aufklärungen gewiß nicht. Vielleicht weil ich selbst zu pessimistisch bin. Mir geht ein "advertisement" im Kopf herum, das ich für das kühnste und gelungenste Stück amerikanischer Reklame halte: "Why live, if you can be buried for ten Dollars?"

In English:

The moment a man questions the meaning and value of life, he is sick, since objectively neither has any existence; by asking this question one is merely admitting to a store of unsatisfied libido to which something else must have happened, a kind of fermentation leading to sadness and depression. I am afraid these explanations of mine are not very wonderful. Perhaps because I am too pessimistic. I have an advertisement floating about in my head which I consider the boldest and most successful piece of American publicity: "Why live, if you can be buried for ten dollars?"

• Freud, S. (1960). Sigmund Freud an Marie Bonaparte, 13. August 1937. In E. L. Freud (ed.), Briefe 1873-1939 (p. 429). Frankfurt a.M.: S. Fischer.
• Freud, S. (1961). Sigmund Freud to Marie Bonaparte, 13. August 1937. In E. L. Freud (ed.), Letters of Sigmund Freud (p. 432), London: Hogarth.