Recently I've faced with the following situation and was really surprised with the rules:
Let's consider the following situation:
A party is located in a quite deep forest. They know that there is an enemy camp within 1 mile away also located in deep forest. One player says: "I'm trying to hide".
In PHB DnD 5e it is explicitly stated (PHB p.177)
When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding …
So he makes a roll and let's assume the final result is 4. Because player can see the result, he can now decide what he is going to do based on this check. Obviously this check is low, and player says: "I stop hiding". It is allowed based on the cite above. After that he can try to hide again and re-roll.
In this case DM can notice that this is a meta game and it is not allowed, because character can't know the roll. In this case, even if this will prevent character from re-rolling directly, it can certainly change his initial plan. Or player can do the following:
Character can make an agreement with his party that he will go behind a tree, hide and then they will try to seek him. In this case it is explicitly mentioned in PHB p. 177 that
Until you are discovered or you stop hiding, that check's total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence. … When you hide, there's a chance someone will notice you even if they aren't searching. To determine whether such a creature notices you, the DM compares your Dexterity (Stealth) check with that creature's passive Wisdom (Perception) score
So even if character doesn't know the roll, he can find "how well he hides" with this "test". This "test" can be made using both passive and active checks. In this case he can definitely find "how good he hides". If somebody in his party could spot him, character is no longer hidden, because that rule above, if not, character is very likely hidden very well (especially if there was a wisdom guy in a party that was by accident unaware of this activity and the check was passive e. g. with fixed known high value). So if character was spotted he just reties to hide until he rolls high enough to hide from his party checks.
So at this moment our hero is hiding and has a really high roll. So he says that he is travelling towards enemies camp in hiding.
Here are rules from PHB p. 182
While traveling at a slow pace. the characters can move stealthily. As long as they're not in the open, they can try to surprise or sneak by other creatures they encounter. See the rules for hiding in chapter 7.
The "chapter 7" rule are the one I mentioned above.
Well, since our hero is hiding and he travels in slow pace, he comes to enemy camp and he is still hidden because he "was not yet discovered" (see cite 2 above).
After that hero says "I try to sneak by those creatures remaining hidden". So since they are not expecting him, they use passive check. Since player already rolled high and that roll value is used against perception checks there is no chance they can spot him, so he automatically (or with very high chance) succeed. In this way he can bypass any guards almost guaranteed.
The same trick can be made with whole party by searching each other and repeating until all are hidden and thus it can be made that surprise is be also guaranteed in first round.
For me it looks like it is 100% correct according to the rules from PHB and it also it looks like extremely broken mechanics. No other check value is known to player before he decides what is he going to do with this ability.
So, eventually:
Is seem broken that player knows the check before he decides what to do with this check. He rolls hide stealth check and only after that he can decide if he, for example, sneaks or attacks.
Is there any fix for this rules published somewhere?
P. S.
I think any check should be made at the moment the check is really needed and each moment it should be checked independently.
So in this case you don't roll when you trying to hide. You roll each time you can be spotted, also you roll on each action you perform, e. g. sneak by e. t. c. because all other checks are performed in the same way.
Again even if you somehow block a party from doing that, player won't try to sneak by a group of goblins when he knows ahead that his roll value is low and already determined.
P. P. S.
I've also checked several forums and videos and everywhere it is explicitly stated that you make check when you hide and you use this single value to compete perception checks and you remain hidden until you found or you stop hiding. Also everywhere it stated that you can move and sneak while hidden and use that roll value against perception checks. So I am really confused.
Best Answer
You're missing the most important part of the Hiding rules.
The players can propose hiding in a particular way but the DM has discretion to say whether it will work.
So here's how to adjudicate this. If you have someone else helping you hide by standing some distance away and telling you if they can see you, then you are making your Stealth check with assistance, and can apply the "Working Together" rule:
Why can't they do this hide-and-seek trick, though? Because if it were that easy, everyone would do it. If there's no additional cost to it*, it's safe to assume that it's the normal level of effort implied by an ability check. They can make the check with advantage because they're working as a team, but at some point they're going to think they're safely hidden, and then they have to sit tight and see if it works.
However, the biggest problem with this scenario is that they're playing hide-and-seek and then traveling. So they're spending time finding their perfect hiding spots and then that's supposed to somehow help them stay hidden when they walk ten miles? That doesn't make any sense. It doesn't matter where they were hiding before they left.
The travel pace rules say that when traveling stealthily, you can try to surprise or sneak past any other creatures you encounter--not that you can automatically succeed at it. So at the time they encounter other creatures on the way, they can roll their Stealth checks to see how well hidden they are at the time they come into contact.
*Just because someone's going to say it: No, "time" is not a meaningful cost, unless spending the time actually puts you in danger. If the DM is not at least rolling for wandering monsters or ticking a clock, you're probably not in danger.