Compatible friends
My 9 year-old daughter's friend spent the weekend with us and it didn't go too well. They are so different, even in basic things like energy levels. My daughter loves to bike, play outdoors and engage in other high energy activities. Her friend is comfy just snuggling with her Game Boy for hours. Soon, my duaghter was getting annoyed with her. She told me that her friend is much more fun when part of a group of friends than alone. I was impressed that she came to that conclusion. I guess the friend needs lots of encouragement to increase her level of energy.
Of course I've had friendships that have weakened when tested that way. We took a dear friend skiing many years ago and after living in the same condo for four days, that friendship was not as strong. One on one for long periods tends to draw our attention to little annoying quirks and habits. I'm sure they notice ours too!