Both of you're statements are valid. If an attacker has access to your device you are *severely* compromised and you can't do much. I am going off the idea that your password manager clears your clipboard history however, but this is a valid and true statement. The thing is: nothing will be 100% secure. Ever. But if we evolve our security at the same rate loopholes, etc are being found, we can prevent data breaches, identity theft, etc. Before it even happens.