Hi, Joed8888! The thumb should be pointed toward the ceiling and not the headstock. There needs to be space between the palm of your fretting hand and the guitar if the hand is to move freely about the fretboard. If you have your thumb flat against the guitar and pointed toward the headstock, that pulls your hand up until it's cupping the guitar, which will make moving the fretting hand difficult. Check out this tutorial for more tips on correct thumb placement. Good luck!