Well, here is an example if you're curious:
Last night a PC in my game failed his save and is afflicted by Lycanthropy. Now, I know he
has it due to the failed save, and I know a
remove curse can get rid of it, but there is nothing in the rules about anything more. This is all there is:
View attachment 261891
How do they know they're afflicted? They need to know before they can choose to resist or embrace.
What about changing before the full moon? Can they resist it before then when the moon is full, or is it
just the full moon? How many days is that?
Now, I can answer these questions easily myself, but for a newer DM I can see how they might feel a bit lost and wonder where are the rest of the rules on this? Is it in the DMG? Nope--nothing there I've ever seen.
So, while the rules for contracting and removing lycanthropy are there, the rest is missing and left up to the DM.