“I can’t remember the title of the book we were supposed to read, let alone the details of the story.” In sentences like these you give a lesser example of something first, followed by “let alone” and then the greater example. But people often get this backwards, and put the greater example first.
The same pattern is followed when the expression is “much less”: “I can’t change the oil in my car, much less tune the engine.” The speaker can much less well tune the engine than he or she can change the oil.
Another common expression which follows the same pattern uses “never mind,” as in “I can’t afford to build a tool shed, never mind a new house.”
See also “little own.”