This phrase comes from Ivorian French speech, where je sais que tu savais pas is used as a light, teasing way to point out that someone has just discovered something obvious or surprising. As a short voice clip, it has circulated among French-speaking creators and group chats as a reaction sound, valued because the wording is instantly understood and the delivery feels like a friend calling out a gap in knowledge. Its staying power comes from that everyday situation: there is always a new fact, twist or gossip to react to with a knowing smile.