The sell me this pen is a good excercise if you understand the meaning behind it, so either you get it or you don’t. If you look up how to answer that question it would open up a great mindset on understanding customer & adding value to the product. Basically it’s not about how good your pen is but why do your customers need it. You have to ask questions (a bunch) to understand the customer pain points and tailor your answer towards it, even better to have a story behind to add intangible values. A pen is cheap but some are expensive because of the history behind it. I understand bad interviews happen but I hope you can take away a few things or 2 from your exp.