According to The Evolution of Useful Things, what caused the popularity of Post-it notes?

Being able to have a sticky piece of paper and to have reminders or good notes on it

Allusion and illusion. an allusion is an indirect reference, whereas an illusion is something that is unreal or incorrect. each of the nouns has a related verb form: allude “to refer indirectly to,” and illude (not a very common word), which may mean “to delude or deceive” or “to subject to an illusion.”