In all affairs — love, religion, politics or business — it’s a healthy idea, now and then, to hang a question mark on the things you have long taken for granted.

Bertrand Russell
Bertrand Russell (1872-1970) English mathematician and philosopher
(Attributed)

Widely attributed to Russell, but not found in any of his online published works or cited to any source.

There are numerous variations on this quote, e.g.,

In all affairs it's a healthy idea now and then to hang a question mark on the things you have taken for granted.

And mixes and matches between those two.

Earliest references of long-form quotation I could find: I also found in Alexander Chittick, Social Evolution, "The Evolution of Capital and Labor" (1919), regarding the plight of laborers:

They should be taught [...] to take nothing for granted in love, religion, politics, or business.

The combination of taking for granted and the same list of four affair topics seems more than coincidence. Was Chittick riffing off of an unfound Russell comment? Did someone attribute a variation of Chittick's passage to Russell? The answer is unclear.