Earlier quoted context omitted.
Why would you need to write your password on a post-it note if you use a password manager? Also, why would the note need to be specifically "on your desk"? If I really had no other choice than writing down a password, I would keep it in a more subtle/hidden place (my wallet, or my phone case, or in my locker). That's still not secure against a targeted attack, but I wouldn't be the lowest hanging fruit at least. Also…
I only use a password manager on my work computer because my boss forces me to. I find your question more surprising! Why would you use a password manager voluntarily? It's a torture device. I use it because my paycheck depends on it. What's your excuse? If I care about a service, I care enough to remember the password. Everything else might as well be a post-it-note on my desk... Though I prefer a simple one-word pa…
I use a password manager in my daily life because I have 3 e-mail accounts, two domains, a cloud service not tied to any of my E-mail accounts, two banking accounts and the need to sometimes log into my wife's account (because she asks me to while she's at work), one PayPal account, and other services for which I wouldn't dare to write down the password to, nor would I dare to use the same password (or slight variations) for them. Using a password manager makes all of these easy to use at the click of a button, without me needing to remember any.
Post-it notes get lost, thrown away, burn, suffer water damage, and are bothersome to copy for backup purposes. Online password managers take care of backing up the DB for you, or if you don't trust them, offline solutions as pass or KeePass (and variations) let you backup the DB on offline drive and store them safely while you continue to use the main DB.
What's your excuse?