If you didn't set the password, someone else did, and it's to keep others out. If you set it, and forgot that you did, you're stuck. The whole purpose of a password is to make it so difficult for someone who doesn't know it to break into whatever - an app, the phone, a website - that what you get for breaking into it is a lot less than it cost to break into it. (Time on a supercomputer isn't free.)
That's why everyone should run a password app, so as soon as you enter a password into anything, you also enter it into the password app. Then, 5 years later, when you don't even remember that you had the <whatever>, you look it up in the password app and bingo - there's your password.
We did that back in the 70s, when people started writing programs requiring passwords (there were probably earlier programs that did, but I never ran into any before the late 70s). But that was for computers! Yep - and a tablet or phone is a computer - and some of them can even make phone calls. But 95% of the device is just a plain old computer, and should be treated the same as the one that locks you out of the server room at work unless you have a key, fob, or know the number to punch in. We're all walking around with computers now - but almost everyone thinks of them as phones/texting machines/social networking machines/ that happen to have some kind of computer-like functions.
Then you forget that you put a password on something, or you forget the password, and that very important data, without which you're going to lose a very important court case, is gone.
Turn your mind around and start thinking of that phone as a computer, and handle it the way you would handle any computer with valuable information on it. (Which includes backing up anything that might become important in the future. Cloud accounts are free - use a dozen different ones if you need to back up that much data. But the prime rule of computing is back-it-up.)