An informal phrase meaning 'to anyone' or 'anybody' — used mainly in affirmative sentences (e.g., 'anyone can make mistakes').
誰にだって失敗はあるから、あまり自分を責めないで。
Everyone makes mistakes, so don't blame yourself too much.
そんなことは誰にだって起こり得るよ。気にしないで。
That can happen to anyone. Don't worry about it.
誰にだって悩みはあるから、話してみると楽になることもある。
Everyone has worries, so talking about them can sometimes help.