Does it always get more difficult to introduce new members?

Without going into all the complicated details of additions to my cat family, it seems to me that it has got harder and harder to introduce new members. I have plenty of space, and three of the cats go out for a few hours each day, but as each new one has come along the introductions get longer and longer. I still have one who lives in my bedroom after a year and is not tolerated by most of the others. Is this a normal phenomenon? I go through all the recommended procedures, and have tried re-introducing, to no avail.

How many cats do you have?

You may think there's enough space, but the resident cats may have a different view. They have figured out their hierarchy and time sharing strategies (cats time share space). Adding yet another cat changes the balance and agreements the cats have established between themselves for keeping peace and confrontations to a minimum.

Marilyn Krieger, CCBC

I have never had issues! I have a lot of places for the cats to get away from each other. ALL of my cats get along well with each other. Its been a while since I introduced an adult cat into my group, but kittens do just fine being introed.

Right now I have 8 cats of my own who live in my part of the house (including one who has my bedroom to herself) and three who live in the guest wing and may or may not be eventually introduced to the others. One of the 'guests' is a stray with an injured paw who was fighting my cats in my garden and my fields until I caught him and treated him, the other two are kittens who are waiting to be adopted.