Sensed Condition = Enemies are flat-footed
Unseen Condition = Enemies are flat-footed
Sneak Attack = Extra damage vs flat-footed enemies
BUT, specifically the Sneak action for the Stealth skill (this is not mentioned anywhere else) states:
You can attempt to move to another place while becoming or staying unseen. Stride up to half your Speed. (You can use Sneak while Burrowing, Climbing, Flying, or Swimming instead of Striding if you have the corresponding movement type.)
The GM rolls your Stealth check in secret and compares the result to the Perception DCs of creatures that you were sensed or unseen by at the start of your movement. You automatically become seen if you don’t have cover or aren’t concealed from them at any time during your movement,
or as soon as you do anything other than Hide or Sneak. The GM might allow you to perform a particularly unobtrusive action, activity, free action, or reaction without being noticed, possibly requiring another Stealth check. If you speak or make a deliberate loud noise, you become sensed. If you do anything else, you become seen just before you act. For instance, if you attack a creature you’re unseen by, that creature is not flat-footed against that attack.
If you’re unseen by a creature and it’s impossible for that creature to see you (such as when you’re invisible, the observer is blinded, or you’re in darkness and the creature can’t see in darkness), you automatically treat the result of your d20 roll as a 20 against that creature on your checks to Sneak. You also continue to be unseen if you lose cover against or are no longer concealed from such a creature. Acting to do something other than Hide or Sneak makes you sensed instead of seen. If a creature senses you via Seek, you must Sneak to become unseen by it again.
Success: You become unseen by the creature (or remain so) during your movement and remain unseen by the creature at the end of it.
Failure: You’re seen by the creature throughout your movement and remain so. If you’re invisible and were sensed by the creature, you’re still sensed throughout your movement and remain sensed, but you aren’t seen.
This is incredibly confusing:
1. You need to read entries in the Rogue chapter, skills chapter, playing the game (senses) chapter, AND conditions chapter to figure out how Sneak Attack should function.
2. Flat-footed yields a -2 AC, but as soon as you attack someone, they lose Flat-Footed.
3. The way I interpret this (but as I said, it is confusing) you need Invisibility, a Darkness effect, or something similar to be able to make a SNeak Attack from Stealth (none of which the Rogue gets).
Am I interpreting this correctly? Is this by design? If so, you get 1 Sneak Attack at the start of a fight. After that you MUST Flank to apply Sneak Attack damage on a Strike. This goes against the description stating that Rogues are intended for striking at targets at the back, at high value targets; you better stick with the Fighter if you want those Flanking situations, and the encounter better not start before you are in position, because your ambush cannot wait until round 2.
I am not saying this is wrong or unbalanced, but some clarifications and better wording is definitely warranted.