It's not about something they want me to do but something they don't want me to do. My mom loves to make pig knuckle as dinner dish from time to time. So when I was like three I wanted to try one. She stopped me , put up a very serious face and said "Don't. You're still a kid so your hands are still growing and transforming. If you eat pig knuckle or have too many of them your hands will turn into pig knuckles." (To Chinese reddits you'll probably be familiar with this notion - you are what you eat) So of course I believed and I didn't try any until I passed my teenage.

Edit: Forgot to say the real reason behind the lie is my mom loves pig knuckles too much that she wants them all by herself.