If you're talking suspension design and use the the phrase ‘virtual swing-arm length’, it’s very likely that people will immediately assume glazed-eye expressions. Start talking about ‘virtual centres’ and the conversation is likely to immediately switch to some topic that sounds much more friendly!
But these ‘virtual’ parts of suspension geometries are actually not at all hard to understand. Furthermore, they can be extremely useful in picturing (and predicting) suspension behaviour. Finally, they are an important ingredient in understanding roll centres – another topic for eye glazing!
One of the problems is that most textbooks start off with complex, real-world suspension systems – and then apply the concepts to those systems. I think it’s a lot easier to start off with the absolute simplest suspensions, where these ideas are far more self-evident