I, for one, tell them one thing, which is 100% true in my honest opinion. Something has value, if (and only if) there are interested group of people, who think it is valuable. Gold is valuable, because human kind has been putting it on the pedestal for thousands of years and cherished it. Lets put the rarity of the metal aside from all this. And money (as in cash) is valuable, because our governments tell us that it is and that you can buy stuff with it. Why is bitcoin valuable? Same thing...people hold it dear and they cherish it for some reason or another. Still, it is a bit different from money as such, because governments still didn't accept it as a payment method in full. If they do, the value could skyrocket, because people who don't believe in crypto, will come into the game (because their governments told them it is valuable).