A zen story tells of a monk named Tenno who had just completed his apprenticeship to become a zen teacher. One rainy day, he went to visit the master Nan-in. As is customary in Japan, Tenno removed his shoes at the vestibule of the master's home.
Nan-in welcomed him in, and they sat down. After an exchange of greetings, the master said, "I was wondering, did you leave your umbrella on the left or the right of your shoes?"
The monk could not answer. Perhaps he had arrived with thoughts about what he wanted to say to his teacher or was nervous about the meeting. Perhaps he was thinking ahead to how his teacher would congratulate him on his promotion. In any event, Tenno had paid no attention to where he had left his umbrella. Realizing he still lacked awareness, he put off teaching and resumed his apprenticeship....
The best way to remember where we put things is to have a place for them. As the saying goes, "All things in their place, and a place for all things."
Therein lies the key.