I learned this the hard way when a friend’s Bitcoin was flagged by a chain‑analysis company. He had bought it years ago, and some of the UTXOs were from a known exchange that had been hacked. His coins were ‘tainted’. He couldn’t spend them without paying a premium to mix. Monero doesn’t have that problem. Every coin is indistinguishable. That’s not a luxury; it’s the definition of sound money. Satoshi understood this early on. He wrote about it. If you want to revisit his original thoughts on fungibility, this annotated compilation is indispensable.