it is, which means we are also aware of its limitations. Our memory is basically one big book, and the art of memory focusses on how to most effectively write in that book. One thing that it is limited in, is reminders. You can’t write things in a book and expect it to remind you of it, you have to open the book itself.
However, Antelex is also onto something with his comment on habits. You might forget a few times at first, but down the road you will be able to better remember that you had to do something that day. Something that can help with that is actually visualization.
Let’s say you have a meeting on saturday, at 13:00. You can already visualize taking a walk during the morning, no phone, but you do bring a watch. You then maybe go out for a meal at 12:00, so visualize that. After the meal, you head to your meeting. Visualizing all that turns it into a plan. Walk until 12:00, eat until maybe 12:45, then meeting from 13:00. Or mind is pretty decent at those.
In the extend of that, it helps to plan things after certain rituals in your life, hence I put it into my example to be after lunch. Maybe you have a weekend morning routine where you wake up, eat, brush your teath, go for a run, shower, and maybe some other things. Generally, at the end of the routine it will be around the same time. You might always start your routine between 7:30 and 8:00, and it ends between 9:30 and 10:00. That means you could plan a meeting at 10:00 and visualize it as a part of your routine that day beforehand.
It might not be waht you expected, but I hope it helps