You might remember the meaning of the character 只 with this easy mnemonic:
You have a large family. You have eight (八) mouths (口) to feed. "Wow! How do you manage to feed and take care of all your children?" your friend asked. "It's easy. There are only eight of them," you replied.
Using mnemonics to remember the meaning of Chinese characters like has a huge impact on how long to learn Mandarin it takes.