Neonchameleon
Legend
The Sage Advice Compendium provides the following response by the 5e designers to clarify what that meant:
To be surprised, you must be caught off guard, usually because you failed to notice foes being stealthy or you were startled by an enemy with a special ability, such as the gelatinous cube’s Transparent trait, that makes it exceptionally surprising. You can be surprised even if your companions aren’t, and you aren’t surprised if even one of your foes fails to catch you unawares.
Surprise is:
And see my replies to others above. The designers didn't intend "threat" to read as anything other than "an opponent on the other side of combat," and surprise was intended to represent an ambush where all of one or both sides are hiding with Stealth to catch the other side unaware and startle them.
- Being caught off guard
- Failing to notice foes being stealthy
- Being startled by an enemy with a special ability
- All of your foes catching you unaware
Your second bullet point is a misrepresentation. You say "Failed to notice foes being stealthy" - but the actual thing you are trying to summaries starts "Usually". Which means that there are explicitly times that the rest of the sentence doesn't cover. Also your bullet points lack indenting so they provide a misleading representation.
A better summary would be
- You are surprised when you are caught off guard. This can be because:
- You failed to notice foes being stealthy
- An enemy has a special ability that surprises you
- Other unusual circumstances that are not covered by the above two options.
- Surprise works at the level of the individual not the group; one person can be surprised when their allies aren't and vise-versa
- If one foe alerts you the attack is coming you are alerted.