A blackboard is read as public learning — what is shown to everyone and later wiped away. Writing on it points to sharing what you know; being called up to it to feeling exposed.
Where in your waking life have you met something like this lately?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.