Week three and my resident cat still hisses on sight. Have I ruined this?

Brought home a 10 week old kitten three weeks ago. My resident cat Alfie is 5, neutered, has been an only cat his whole life and frankly it shows.

I'll be honest about my mistake up front: the first two days I just let them "work it out" because that's what we did growing up on the farm and it always seemed fine. It was not fine. Lots of hissing, one proper swat, Alfie spent a day and a half on top of the wardrobe glaring at everyone including me.

Since then I've done it properly, kitten has her own room, I swap blankets between them, they eat either side of the door. But any actual sighting = instant hissing and Alfie leaves the room. The kitten is completely oblivious and just wants to play, which somehow makes it sadder.

Three weeks feels like forever. Did my botched first 48 hours poison this permanently? Anyone come back from a bad start?

You have described our first TWO MONTHS. Otis (resident, grumpy) treated Millie's arrival as a personal insult. We also botched the start, and we also went back to basics with the separate room and the blanket swapping.

Week 7 was our corner, and it turned on food. We fed them in sight of each other at a big distance and moved the bowls closer by maybe 30cm every few days. Hissing at week 3 with no actual fighting is honestly on schedule, not a disaster. Eleven months on they sleep touching, which I'd have bet money against.

One thing that helped my sanity: I stopped counting hisses and started tracking "can they be in the same room doing normal things." That number only went one direction, even on days with plenty of hissing.

Hissing and leaving the room is your big cat choosing to walk away instead of fight. That's not failure, that's him being sensible. The oblivious kitten thing is universal, they have no idea they're being insulted.

Kevin, the reassuring news from years of doing this badly and then less badly: a rough first 48 hours is recoverable, and the recovery is exactly what you're already doing. I've settled in rescues who arrived with far worse first impressions than one swat and a wardrobe sulk, and the slow route worked every time. It just worked at cat speed, not human speed, my most stubborn pair took the best part of three months to declare peace.

What you've described, hissing on sight but eating either side of the door and no injuries, is a normal middle stage, and the step-by-step version of where to go from here (short supervised sessions, feeding at a distance like MillieAndOtis describes, retreating a step whenever things spike) is laid out in the site's guide to introducing a kitten to other pets. The signs things are actually going wrong, real fights, either cat off their food or avoiding the litter tray from stress, are in there too, and if you ever see those it's a vet or behaviourist conversation rather than a wait-longer one.

Also, small thing, but give Alfie some one-on-one time that the kitten can't interrupt. The resident cats who come around fastest, in my experience, are the ones whose routines changed least.

Update for anyone who finds this thread mid-panic like I would have: week 10 now. They nap on the same sofa, opposite ends, a truce Alfie pretends is a coincidence. Occasional hiss when the kitten forgets herself. I've stopped counting them like MillieAndOtis said and honestly that advice did as much for me as for the cats.