To use an obvious example, if you log into an account you've previously logged into directly from your home computer.
More broadly, any privacy tech can be undone by poor 'operational security'. For example Ross Ulbricht - 'Dread Pirate Roberts' of Silk road - posted on StackOverflow under his own name to ask "How can I connect to a Tor hidden service using curl in php?" [1]
[1] https://arstechnica.com/information-technology/2013/10/silk-...
Re:Tor Browser 9.5
by calvinmorrison on Tuesday June 02, 2020 @02:15PM
(#23394128)
Well a big one would be putting personally identifiable information on websites inside or outside the tor network.
https://blog.torproject.org/browser-fingerprinting-introduct...