You have not provided any rule that says the initial role isn't all that is required to stay silent forever.
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A single roll at the beginning is all that RAW requires in order to be silent the entire time. This ongoing effort thing is nothing more than assumption and rules additions on your part.
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There is no rule that says there are ongoing efforts to try and hide and if you don't do that, you come out of hiding.
This can't be right.
For instance, if a character uses an action (or a bonus cunning action) to make a DEX check to hide, and then starts beating on his/her shield with his/her sword, s/he doesn't remain silent. Hence s/he doesn't remain hidden (SRD p 80: "you give away your position if you make noise").
As I understand it, this is the point that [MENTION=6787503]Hriston[/MENTION] is making - that to remain hidden, you have to maintain the conditions that ensure your position isn't given away (eg you must refrain from deliberately making noise, you must remain from deliberately providing visual cues, etc - the DEX roll tells us whether or not you
inadvertantly make noise or provide visual cues).
As I understand it, the point of the elf or halfling abilities is not that they can be simultaneously hidden and noticed (which would be an absurd contradiction) but that they can be hidden in conditions where most people would be noticed. When
Sage Advice says
The lightfoot halfling and wood elf traits—Naturally Stealthy and Mask of the Wild—do allow members of those subraces to try to hide in their special circumstances even when observers are nearby. Normally, you can’t hide from someone if you’re in full view. A lightfoot halfling, though, can try to vanish behind a creature that is at least one size larger, and a wood elf can try to hide simply by being in heavy rain, mist, falling snow, foliage, or similar natural phenomena. It’s as if nature itself cloaks a wood elf from prying eyes
it seems fairly clear to me: normally you can't hide if you're in full view (
invisibility, or some forms of distraction, might generate exceptions to this general proposition), but an elf in a mist or snowfall is
not in full view. Rather,
nature itself cloaks the elf. As long as the snow continues, the elf will continue to be cloaked, and hence will remain hidden (as long as s/he doesn't deliberately make noise or provide visual cues, and as long as the DEX check is successful and hence s/he doesn't inadvertently make noise or provide visual cues).
I would think it is obvious that, in so far as the elf remains cloaked and hence hidden, s/he is not being observed. People might be looking - even staring - in his/her direction, but if nature is cloaking the elf and the elf is neither deliberately nor inadvertently providing visual cues then s/he is not being observed.
Hidden is basically synonymous with
concealed from sight!