Because when you make a payment, the whole prehistory of the bitcoin you’re sending is traceable back to the very first transaction. If you don’t follow basic rules, your transaction could be linked to you, making all your past and future transactions visible to a third party.

Some simple rules to follow when sending:

• avoid using KYC bitcoin (i.e. bought at a centralized exchange like Binance)
• coinjoin your bitcoin with Wasabi or Samourai before sending
• use anonymous swap exchanges to break the link between the sending and the receiving address.