This explains why 5th edition doesn't just carbon copy an earlier attempt at H&S rules. It does not explain why it does such a disastrous job.
I dunno. I have no problems with it. You take the HIDE action to be HIDDEN. Seems pretty straightforward to me. What they really needed to do was spell out HIDDEN as a condition, in the conditions list. Personally I figured that it was pretty self evident, but, apparently not.
IOW, if you don't take the HIDE action, you cannot be HIDDEN, and nothing about being HIDDEN applies to your character. You might be invisible (which is spelled out as a condition) but you aren't HIDDEN.
The problem comes when people try to conflate the two things.
thethain
I was kinda miffed when in the middle of a campaign I was told my goblin couldn't try to hide behind a wall because "They know you are here now".
Next campaign I just skipped the whole thing and picked halfling, Hey a creature, I will attempt to hide, since my racial feature states explicitly that is what I can do.
Read more:
http://www.enworld.org/forum/newreply.php?do=newreply&p=7080681#ixzz4eAm0VvT3
That's just poor DMing though. If they don't have a line of sight to your character, you can hide. Now, since you're hiding behind a wall (depending on how long the wall is I suppose), they are going to know where you are, even if not the exact square, and, as soon as they move around the wall, they are going to see you since now they have a clear line of sight.
And, it's not a terribly bad call to say that you wouldn't get Advantage on your attacks for ducking behind a wall. I mean, they DO know where you are, even if they cannot see you. As soon as you poke up to shoot your bow or whatever, they are going to see you. There's no reason you'd gain Advantage on attacks.