I am hoping this is not a Bad Sign. I have an acquaintance who has a cat who ALWAYS hides, ALWAYS. She says she wouldn't even know she HAD that cat except for his vet bills and litter box and food dish. That would be...a disappointment.
On the encouraging side, my family growing up got a cat who hid at first but then eventually joined the household proper, with no further issues to speak of. Well, no further issues beyond a lifetime of various neurotic behaviors.
Also on the side of encouragement is that our cats who have gotten themselves in trouble (trying to escape outside, attacking each other, etc.) have been the cats who incorporated nearly effortlessly/confidently into the household, all but kicking previous feline residents to the curb.
And this new cat has only been with us for five days. I know it's not time to panic yet. But I find I can get quite a bit of pre-panicking done if I start early. I see this cat-hiding thing as the first segment of many, many potential futures branching ahead of us, many of which turn out fine but some of which include Later Woe. (Anecdotes from all kinds of branches are welcome.)
I wish pets had little gauges on them, so I could determine if, for example, the cat is just adjusting slowly/normally and/or this is just his temperament---or if he's permanently miserable here. Like, if he's going to be the sort of cat who prefers to stay contentedly out of sight in pleasant quiet nap nooks, and maybe only come upstairs after the children are asleep, that's fine and also I wonder if I could join him. But if he's cowering miserably, flinching at every sound, and would thrive and be happy in a quiet household with two adults and no cats or children, that's not fine.
I would be perfectly content
if you'd leave me alone with my dishpan.
Or maybe I'm miserable
and you should spare me the agony of your family life.
He doesn't have a name yet, and there's a story behind WHY, and that has to wait because it's time to get ready for swimming lessons.