There is no such thing as 100% anonymous. If nothing else, your anonymity set is the set of people using Monero. Some people don't use Monero. Monero may also have bugs. Even if not, ways may exist to infer some information through Monero's privacy layers, either now or later. Attacks only get better. If you wear a seatbelt, you can still die in a car crash. Use common sense, prudence and defense in depth.
