This is especially true for a high number of time demands.
The reason for peace of mind is simple, and it starts at the moment when a time demand is Emptied from a Capture Point. If the time demand is converted to a segment in your Schedule, then you have set time aside in the future to get it done.
If the time demand is added to a List, then you have also implicitly set time aside to get the item done in the future, but there is a major difference from the prior option.
When the item is added to a Schedule, you can forget about it until the date/time approaches as long as you have a reliable method for interrupting what you’re doing to remind yourself to get started.
By contrast, when the item is added to a List, something a bit dangerous happens after it’s added:
1. you make a mental note to yourself of the time that it’s due, or the completion date that would represent a late one
2. you start to make an effort to remember this due date
3. when you check your list each day, you must revisit the item to ensure that the due date hasn’t passed, redoubling your effort to remember
The overall effect is that you must revisit the List to check on the item, much in the way that a mother fusses over her baby while it’s sleeping. This fussing isn’t a problem when the number of time demands is small, but when the total number of items in a List exceeds a certain number, the technique becomes counter-productive.
That’s when we need the relief and peace of mind that Scheduling affords. The moral of the story is that when the number of time demands grows past a certain point, then it’s better to “Schedule and Forget It” rather than “List and Fuss Over It.”