If you've ever tried to estimate how long it will take to paint all the rooms in your house, and had a 'hard stop' for when the project has to be done, you've probably confronted many of the classic challenges of estimating. painting - how much square footage, how many coats, how much preparation required, how much wait time between coats, how much equipment?

Talk about multi-tasking - show how it can detrimentally affect things. Quote some of the research. Then emphasize that if an employee is spending significant time waiting on a constraint which is not under their control yet which prevents progress on their project, the ability to switch to another task is critical for efficiency.

Goal is to get to the point there is a volume of work to do (the 'demand') that you can evaluate the capacity of your team against.