D&D 5E Can someone clarify the mechanics of surprise for me?

[Rya.Reisender]

The closest it gets is when describing the Stealth skill and how to hide, it mentions that creatures (specifically in combat) are assumed to be staying alert for signs of danger at all times, or something along those lines. So it gets close.

Yeah, but that's just another indication - in combat, not always. =p

 

[AaronOfBarbaria]

It doesn't specifically state so in the rules, though.

That's the thing with natural language rules; stating is fine, even if it isn't specifically stating.

And all it takes to get my understanding of the rules is the words that are there, taken in their natural language use; where "even if they aren't searching" and "because they have their eyes open" are functionally the same, regardless of that they could have opted for more specific language.