Why does my chicken go dry when I boil it?

This may seem a silly question, but it has always stricken me as odd that chicken should dry out when I boil it in water. Intuitively it just seems weird, but thinking about this a bit while cooking just now, it also makes little sense to me from a basic physics point of view. I googled this first of course, but I can't seem to find an answer as to why this could be.

Assuming I don't put any salt in the water in which I boil it, the concentration gradient caused by ions and other molecules in the meat should cause the water to diffuse/osmose into the chicken. Furthermore any minor temperature gradient should also be pushing water into the chicken. The most plausible explanation I came up with is that the chicken is over-saturated with water to begin with -either naturally or introduced during processing of the meat- and boiling it then somehow reduces the capacity of the tissue to retain the liquid.

I feel I have to apologize that my first question here isn't anything Higgs related or anything remotely that interesting, but I'd appreciate it if anyone could provide a definitive answer to this enigma, so I can get back to my dinner with my mind at ease.