We tend to dismiss stories as the last resort of people without substance. As an older retiree remarked, “Why, I have a perfect memory. I even remember things that never happened.” We denigrate professors and elders for telling “war stories.”
The argument in that paragraph is that "WE" make the mistake of thinking such people (e.g. professors and elders) are 'without substance', which means they are without enough intellectual capacity to present the idea directly.