I forgot my private key's passphrase, but I use it every day [migrated]

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http://serverfault.com – ...from my Mac. I think Keychain Access remembers my passphrase and applies it every time I log in to a server, but in this instance I can't log in to the remote server directly from my laptop; I have to first log in to a different server and then attempt to ssh to my target. Which doesn't work because even though I have copied my id_rsa to my user dir on the first server and set permissions correctly, it is not automatically decrypted as it is on my laptop and I am prompted for a passphrase. Which I don't know. So my question is: is there a way to retrieve that passphrase from Keychain Ac (HowTos)