Software complexity following an ideal gas law is an analogy that works in a ton of ways… time (you’ll keep adding stuff until you’re running close to a deadline at which point you have to actually decide what to cut), head count (complexity will rise to match the number of people working on it, since people aren’t just gonna sit idle), speed (it’ll get slower until it’s “noticeable” on the dev’s machine, at which point it gets optimized), etc etc etc.

I’ve tried to use this analogy to PM’s who have trouble understanding why adding more engineers to a project doesn’t make it go faster: the software expands to fill its container.