Cách sử dụng
The expression "not be born yesterday" means that someone is not naive or gullible. It implies that the person has experience and isn't easily fooled by others. You can use this expression when you want to suggest that someone is aware of what's going on and won't be taken advantage of easily. For example, if someone tries to sell you a fake product and you don't fall for it, you could say "I wasn't born yesterday, I know that's not a real product."