My sempais tell me this all the time. It's not easy for me...probably because I like to focus intensely and do the best performance possible. It's a carry-over from my previous performing arts work, in which you only relax when the chart calls for a relaxed feeling, such as a slow blues. So, quite a bit of my time in the dojo is about doing the technique in a relaxed manner till I can finally genuinely relax.
I've found that being relaxed is important in most performing areas - both guitar, vocals, and theater.