ELI5 Truffles - What makes them special and so expensive?

Why are truffles such a big deal? If truffles are so rare why don't we just farm them? Did you know that truffles used to be common and much less expensive in the early 1900s?   ... We explain like i'm five!     Thank you to the r/explainlikeimfive community, and specifically the following reddit users whose questions and responses formed the basis of this conversation: harrybro, concise_pirate, irmas, giralnias, letstrythisagain, salt-the-skies, esrgdsger, najjex, thesmitestuff, frankiebignut & peacheserratica   To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]