On to today’s idea… Trying to maintain more than one calendar poses a huge risk. It’s inevitable that some commitment will make it into one and not the other(s). For that reason…
If you must use multiple calendars, however, have clear boundaries so that the different calendars serve different purposes. You might have a digital calendar required for work but then keep a personal calendar for your after-hours life. Or you might have a paper planner for work in addition to the digital calendar. The planner, then, is for tasks, not appointments with people. Whatever boundaries you choose, they will help keep your calendar(s) trustworthy and simple.