In case you ever wondered????

"..there are ... times when you come across a day-to-day application of technology that's so simple and yet so important, it reminds you what all this innovation is about. Case in point: that ubiquitous hole at the top of your BIC pen cap

Article solves the mystery (not what you might think) AND - as an extra bonus - why air plane windows are NOT square.

http://www.sciencealert.com/here-s-why-there-are-holes-in-the-tops-of-pen-caps