I am going to quote from my book, "The Principles of Correct Practice for Guitar", to bring this point home:

"The relative state of tension or relaxation in the muscles is one of the hardest things to be aware of. I once saw a person play with so much tension in her right shoulder that it was up to her earlobe!

Always trying to be helpful, I pointed this out to her when she finished. As she let her shoulder down a few inches to it’s normal position, she told me I was wrong, she wasn’t tense, but very relaxed!

The reason she felt this way is because we very quickly become used to whatever we experience, and consider it normal. We never question whatever tensions we experience in learning new skills on the guitar, and in fact consider it part of the doing of it. And it often is, but it doesn’t have to continue to be that strenuous. We can learn to do the movements with less effort..."
(continued)