There's a good possibility that you've forgotten a password and had to get hints or recover it. But the process for that isn't very trustworthy. Intruders can guess security questions, for one thing. Samsung might soon have a subtler way of helping you remember your password, though: it would give you a palm reading. A recently published patent application shows that Samsung has been exploring a system that would scan the unique lines on your palm and use them to display hints in the form of incomplete characters. You'd get a nudge in the right direction, but nothing so obvious that a thief could guess it (even if they could use your hand).
This could theoretically extend to signing you in, although Samsung would likely want to implement depth sensing or a similar technology to prevent evildoers from cheating with photos.
There's no certainty that you'll ever see this in the Galaxy S9 or any future Samsung phone. It's just a patent filing, and that won't necessarily translate to a finished product. It's a simple-enough concept, though, and it could be extremely helpful if you're struggling to get into an online store or are worried that you've locked yourself out of your phone.