Before this switch i would default to using memory. It was easy, it worked, and i have a rather good memory. Most things worth remembering somehow just "sticks" without any mnemonics.
After the switch, i got 10x the information i used to get before, and while i initially settled on using my inbox as a "todo list", flagging items that needed attention, this also became rather inefficient after a while.
I started keeping a journal. Every meeting i go to, i jot down notes, every agreement is written down. I still keep my todo list, but it's in Emacs org-mode now. Notes are handwritten.
As the author also hints, handwriting helps commit things to memory, so the times i actually consult my notes are rather rare. Instead, by simply having written them down, my brain somehow accepts that "it's under control", and focuses on something else, but still remembers it.