I agree with
Carlo Villa... write it down, use a password manager, or use a password that's familiar to you... one you've been using for years. Why people use "new" passwords is beyond me. Make it simple for yourself... it'll still be hard for anyone that doesn't know the password. My fingerprint backup password is the same one I use to unlock my computer every day. Never will forget it!
That said, you can sign in to
Android Device Manager with your Google account on a computer and change the password. It works for some, but not all people who've tried it. If it doesn't work, then you'll need to factory reset your phone... and yes, you'll lose your data.