My Dad tried this when we first taught him to use an ATM and setup his PINs.

He carefully wrote them in the back of his planner which he keeps in his pocket. Then he realized he needed extra security and added some extra digits before and after.

Then promptly forgot which digits to remove and which to keep.

His new approach is: 1. Pick a “famous” battle 2. Hand me a card and ask me to go to an ATM for him 3. Tell me the PIN is the battle of whatever 4. Yell at me for being an idiot for never having heard of the battle, let alone know the date.