Sailis went through 8 years of Hell at such a young age. Do you think he remembers the meaning of that word? Do you think he remembers how it felt?
He would try to remember, to think of a time when he was just a kid living on Alternia. All he could come up with were vague feelings, maybe the occasional memory, if something jogged it. It upset him to think about how much of his life he didn't get to experience, so he didn't try to think about it very often. The truth is, living at someone else's mercy is all he knows. The closest thing to safe he has is when he does what he's told.
Even now, he's living in a highblood's home that other highbloods frequently visit. He's wary of them, of course—anxiety charges him up like an electric current, getting him ready to move, to do something, to watch each little twitch of the face and movement in the shoulders and prepare him for what's coming. But this was a kind of fear he's known. He knows what to do with it. Even if it isn't totally necessary now—he knows how to navigate that kind of stress.
But nothing is asked of him. He's left to his own devices, with no rules and no obligation, completely free to do what he wishes. There's no safety in that. Nothing to make the fear go away. Even when he offers help, asks for a job, something—there's no satisfaction from the highbloods, no grunts of approval or any signals that told him he did what they wanted. He's so scared, all of the time. No matter how many times he tells himself, it's okay, they won't do anything, nothing will happen, he just...he can't believe it.
In the midst of actual, genuine safety, Sailis is terrified.