So many people I work on have head-forward posture from things like using laptop computers. They eventually hold their heads forward on their bodies, at an angle all the time and not just when on the computer.
This means the muscles on the front of their neck and chest are shortened all the time. Which means instead of their skeletal system holding the weight of their head, they use the muscles of the upper back and neck (all of the time) to support the weight of their head.
Just visualize for a moment, if I asked you to sit at a table, put your elbow on the table, and hold your forearm perfectly vertical.
If I then gave you a bowling ball to hold in your hand, you could possibly hold it quite a while, as long as you held your forearm perfectly straight up (your arm bone supports all the weight).
Now imagine if I asked you to hold your arm out at 30 degrees, and hold the bowling ball. You would likely set it down very quickly as your biceps tried to hold the weight of the ball.
I had a patient a couple years ago whose initial assessment was "all twisted up". I worked on him for a couple months, getting him straightened out, only to have him return twisted up again the following week.
I am embarrassed to say it was after many treatments that I finally asked what he did for a living. He replied he worked at a computer every day at work. I asked him to tell me about his workstation.
With a little coaxing, he revealed that his monitor was not only not at eye level, but was over to his right side. He then added that his tower was to his left, and the mouse cord was too short to reach the right side of his keyboard, so he would use his right hand to mouse on the left side of his body...
I explained that he had to change his workstation, to which he insisted he couldn't. I went on to encourage him to at least entertain the idea, and I suggested spending 10 bucks on a "mouse/USB extension cord" would be a lot cheaper than what he was paying me out-of-pocket each week for treatments.
Well, he arrived back the next week saying he had been able to get the monitor in front of himself at eye level, and he had bought the extension, and was now mousing on his right side.
I only saw him that once and he never felt the need to return for treatment again.