You might remember the meaning of the character 密 with this easy mnemonic:
The hunter didn't have the heart (心) to slash (丿) the princess like he was ordered. He deserted her in the mountain (山) and hoped that she would find a roof (宀) over her head. It didn't take long for the evil queen to discover his secret though.
Using mnemonics to remember the meaning of Chinese characters like has a huge impact on how long to learn Mandarin it takes.