Doing this kind of thing is so helpful to get perspective on our life. One part is just writing down all the events we can remember. Then we can add to that some kind of schematic based on longer periods of time, both for understanding the phases of life we've already been through and for having an overarching plan for what's (possibly) left. Decades are one way to do it, but I thought it was fun to use custom timespans to map to my own milestones. Once I made my "life calendar", I've tracked it for longer than I did with any prior planning attempts.