At my level, as a beginner – I’ve been playing for a year and a half, but I still consider myself a beginner, as my progress has been quite irregular – I find there are days when I go to play my shakuhachi and I just can’t get a sound. I struggled with getting my embouchure right for a long time, but I’ve mostly overcome these issues. However, there are times when something just isn’t right and I can’t get a stable sound.
I have allergies, and it’s obvious to me that when I’m having a strong allergic reaction to pollen or other allergens, my lips swell up slightly, just enough to throw things off. Other times, it could be the dry air (it’s autumn now, and the heat is on in my house, which lowers the humidity, but it’s still not much lower than 50%).
When this happens, it can take ten or fifteen minutes for me to get my airflow focused enough, and I eventually do get sound, but it can be frustrating. What I tend to do is just play long notes, up and down the flute, to “loosen up.” The sound eventually comes; I’ve learned that there’s no point in trying to rush it.