Ugh, unlabeled containers are the worst. I saw a thing online where someone used baking powder instead of flour in a cake because the bins looked the same. Total waste. After hearing about that mess from @the_robin's friend, I check my own labels twice. I've had my own near-disasters with the big sack of powdered sugar looking just like the flour. Once you ruin one batch of cookies, you never skip the label again. It just saves so much trouble and money.
My own unlabeled flour bin caused a similar mess last year. I used to skip labels, but @the_robin, your friend's story convinced me to always mark them now.