Notice I said you can't remove it from an ally. I did that to try to head off questions about shaking someone or calling out to them to react.

Although, it is helpful to think of being Surprised as a condition it is important to not confuse actual conditions listed in the back of the PHB since there is no such thing listed.

It seems to be a condition in every way except not being listed with other conditions. As such, by RAW, you can't treat Surprised as a condition I suppose, but it sure acts like one. So agreed, but I'll probably still call it that (sometimes).

Agreed, I think the differentiation lies in the fact that all the real conditions can be applied at any time as opposed to Surprised only very specifically and only once per combat for less than one round. Again, very helpful to think of it as a condition though, helps alleviate its confusion.

@FenrirG That sounds like a new question (and I have an answer).

Not trying to be mean, but I gave you the page number so you could go read it. It's very clear (they use Feral Instinct) and not worth copy-pasting here (since it is not germane to the Q&A). Such a new question should be closed due to lack of research.

Questions might be downvoted for lack of research at the viewer's discretion, but lack of research is not a reason to close a post. In most cases, even the seemingly obvious questions are useful.

Ah, thanks. I couldn't decide between closed and downvoted when I made my comment. Clearly I was wrong. Still fairly new here despite being recently active.

You are not being mean and there is no such question being asked on the site by me. I simply missed the page numbers on my first speed reading the answer.

Mmm. Maybe a little mean, so for that I apologize and will try to be completely civil rather than mostly. I'm just trying to keep this Q&A focused on the characters who are Surprised, and not get bogged down in a few exceptions (in which the characters are essentially not Surprised at all).

In regards to not removing it from an ally, couldn't a character help prevent an ally from being surprised? E.g. the low perception fighter doesn't see the bandit hiding behind a tree, but the high perception ranger does spot him, and yells out "Ambush!" or "On your left!" or "Hit the deck!". Mechanics-wise, I'd think that would give the the fighter either a bonus to a perception check (similar to the athletics bonus he'd get from the ranger aiding him in climbing), or a chance to take a reaction like draw a sword, raise a shield, or lunge for cover. Did I miss a rule that contradicts this?

I think that is special feature or feat territory, not something everyone can just do automatically. However, if you told your DM that you are scouting and will shout out (give up your own ability to hide afterwards) if you find a threat, maybe the DM would give their perception rolls advantage or just allow your perception to help. However, there are no rules allowing for this, so it is firmly in the realm of what the DM allows or doesn't. As a player, you should not expect to be able to do this per 5e rules.

Also, if you're walking through a dangerous fantasy forest, why wouldn't you already have your sword drawn? Your armor & shield only help if you wear them, and your sword only works if it's in your hand. Sure you might put it away to climb a cliff or navigate a narrow ledge, but then you pull it out again when you think you won't need your free hand vs possible attacks.

@NickBrown Why would I have to prearrange what actions I would take in the event of noticing someone sneaking? If my character's perception is high enough that the bandit is not successfully being stealthy to my character, how does their attempt at stealth block my character from choosing how to react when spotting someone hiding in the bushes?

@NickBrown "...why wouldn't you already have your sword drawn?" Because I haven't needed it in the last three days of hiking through this forest, and that's why I bought a scabbard. I think it would be strange for someone to walk around brandishing their sword all the time.