You know how you're in the grocery store and you're standing in front of the spices and you think, do I have cinnamon at home? Maybe your faulty memory extends to allspice, nutmeg, cumin, cream of tartar, dried mustard, tarragon, or almond extract. So, just to be on the safe side, you throw that little jar into your cart, only to get home, open your cupboard, and find 3 jars of cinnamon staring back at you, and then you realize, what you really needed was ginger and thyme. Well, I've done the same thing when I'm staring at art supplies. You know those babies aren't cheap, so when you finally make your decision to buy a tube of Cobalt Violet Daler-Rowney Oil Color and a pale orange Faber-Castell Watercolor Pencil and you come home and see that you've already got them, it's complete buyer's remorse! Not that you won't use them, but there were so many other colors you could have picked up for a relationship. (-;
I got the brilliant idea of writing all my supplies down (not really, but I started with good intentions). Basically I have one brand of oil, acrylic, and the aforementioned watercolor pencils written down. I only have 85% more of my supplies to record.
This tool works fantastically if I remember to bring the notebook with me...which I did for awhile. Then, if you look closely at the stain in the middle of the notebook, the second you forget that you threw a small package of goat cheese in your purse and forgot about it all day long, and it completely reached a beyond-brie-like melted stage and oozed its fatty nature all over your art supply notebook, you decide to take it out of your purse and JUST take it with you when you go to the art store. But then, you're at the art store and you have forgotten the notebook. And guess what, you come home with another tube of flesh tint acrylic color. Drat! Foiled again!