This Daily writing tip today talks of a Syndrome that is ” Negative Guilt Syndrome”, explained as “A reader expresses second thoughts about a sentence he/she wrote. use of a double negative to convey a positive is an unusual construction and remembered the dire warnings received in my youth to, “never use a double negative.”
The negative “cannot fail to” is a softer way of saying, “you must” or “you have to.” A common reaction of English speakers to being told that we must do something is “Oh yeah? Who’s going to make me?” Using the phrase “cannot fail to” instead of “you must” is a way to avoid provoking a hostile reaction in the reader.
A “double negative” results from the presence of more than one negative modifier in the same clause. For example, “I can’t get no satisfaction” is a double negative because it contains not and no.