Mezzanine is a story about thoughts: How many thoughts does the average person have per day? Why do shoe laces snap? What happened to the milkman?
People have the most random thoughts but usually do not spend much time on them. The protagonist Howie, however, uses much of his lunch break thinking those things through, not just philosophically, but as scientifically as possible. He classifies his thoughts, eventually devising a taxonomy of them; he quantifies them, trying to find out how many different thoughts he has in a day or even a year; and, in true scientific manner, he uses the data he has compiled in his head to accurately predict the age when he will have become a complete adult, i.e. when his thoughts are 100% "adult grade" and not contaminated with thoughts from his childhood.
In this regard, Mezzanine is not just a thought experiment or metacognitive novel, but a demonstration of how much scientific thinking is behind everyday items. The only difference is that Howie compiles thoughts that others have had when they designed items such as straws, shoelaces, or milk cartons. Before such an everyday and rather boring item is produced by a machine, someone must have done a fair amount of research and development to optimize the production process and outcome. Indeed, in the end, Howie discovers a scientific paper about evaluating the abrasion resistance and knot slippage strength of shoe laces, which finally allows him to stop thinking about shoe laces and focus on other things at the end of his lunch break.
The extensive use of footnotes illustrates the idea that each thought leads to another, and that all of them are connected (there is even a footnote on footnotes). Some of them are pages long, following a thought all the way to the end before the reader is allowed to return to the main plot only to be caught in another thought footnote shortly after.
The quick succession of Howie's arguably useless thoughts may be the result of his being trapped in a consumer-oriented, capitalist society where all he does in his regular 9-to-5 office job is working on mundane and effectively meaningless tasks as part of a zombie-like workforce. Even office conversations follow a set of unwritten rules, where all parties involved know exactly what the worn-out cliches really mean but use them anyway because they are part of office culture. The same goes for cashiers in a convenience store, who give every customer the same superficial smile. The idea of essentially useless work is emphasized by Howie's thought about the men's room, calling it the only place where people know what is expected of them. Howie's thoughts imply that particularly in large organizations office clerks tend to lack goal orientation and therefore focus, which makes their work appear meaningless.
