I just spent a bit of time looking for the source of this quote, and I've found that sources simply cite "Winston Churchill, Reader's Digest, December 1954" when they present this quote (see here, for example, and it's on page 77 in case it doesn't work properly). I thought maybe Churchill wrote an article for Reader's Digest in December 1954, but nope -- while he had been published (or at least tried to publish) in Reader's Digest before, he did not do so in 1954. Indeed, it would have been odd for the author of the above source to not have named the article had Churchill written one. It appears that Reader's Digest simply quotes him, and obviously if they had cited their source, then future scholars (as well as "quote websites") would have cited that instead of Reader's Digest. Of course, I don't have access to the magazine (I did look it up online and could see its table of contents -- nothing but Christmas stories, which you would expect for a December issue of Reader's Digest from back then, when they mostly did stories), so I can't verify exactly in what context they quote him. But I would have to say, without finding a more adequate source, that I could not confidently present this quote in an academic paper. Maybe he said it, maybe he didn't, but citing a Reader's Digest "quote" is not very scholarly.