This is a famous saying of Hanekawa Tsubasa.

Hanekawa Tsubasa, the protagonist in Ishin Nishio's "Fairy Tale Series" light novels and its adaptation animation, is a girl who is fascinated by cats. Monitor Araragi Koyomi, with good conduct, excellent grades and serious personality, is the monitor of the monitor and is called the monitor's sister by Oshino Meme. The mantra is "I don't know everything, I just happen to know".