I forgot one for a BTC wallet late last year. It wasnt fun but I remembered it after trying combinations for a few days. You have to be very careful.
Not backing up your wallet and losing or forgetting your passphrase are by far the easiest ways to lose your BTC. If your wallet is locked with a decent passphrase and backed up its 99.9999999999999% safe.
Also, consider the possibility, if you have a family, that something could happen to you. Plan for such a contingency (e.g., leave an envelope with passphrases for your wife in escrow with a 3rd party)
I think not made backup it, but I forget wallet number not my password