Be honest now. I've been playing for 30 years, and I have never met a player, including myself, who could honestly answer no to that question. There are a few things that are always true when we are unable to play something we want to play on the guitar. One of the things that you will always find, if you look for it, is what Arron Shearer called, in his first book, uncontrolled muscle tension. Many, many players have in fact commented on this fact, mainly because this fact becomes obvious to anyone who plays for awhile, pays attention, and starts to discover the path to gaining increasing ability on the guitar.
Many people mention it.
No, it seems most people would rather try to play that bar chord or that scale with their shoulders tensed up to their ears, their pinky tensed up and pulled 2 inches from the neck as they dislocate their shoulder trying to get it to it's note on time, practice and play that way day in and day out, and then wonder why they find that scale hard to play, that it breaks down at a certain speed. Or maybe they wonder why they have a pain here or there. Hell, they may be really persistent and keep at it till they qualify for this new disease I'm always reading about, Repetitive Strain Injury. I got a new student about a year ago, we'll call him Tom. Now Tom had been teaching himself for a few years, is very musical, very intelligent, and managed to learn fingerstyle guitar well enough to attempt some rather challenging pieces, including some classical repertoire.