Interjection from me: No child has ever died in a shared double room, not even in their teenage years. You can see it by all the mentally disturbed people from the generation where that was still standard. Quarrelsome bunch that only looks out for themselves and doesn't like to get along with other people... hmm, no, wait, somehow not.
Of course, here in the house building forum, (prospective) families mostly build so that the dear little ones can have their own spaces and a nice garden. The benefits of having separate rooms and the drawbacks of shared rooms are often greatly exaggerated.
As a person, you can also develop the ability to make the best out of suboptimal conditions through compromise. That can sometimes be helpful later in life. And I can sing a song about the generation of self-centered individuals who always had their own rooms!
(no, you don't automatically become like that just because you have your own room. That was an exaggeration.)