They tend to live in thorny thickets that are nasty walking. If you are lucky enough to find them, often the best you will do is to hear them flush. If you see them flash through the woods you are even luckier, if you get a shot it's a day for celebration, and if you actually connect and bring one down you feel like you won a gold medal. Good luck finding it once it's down, too! Good dogs make all this easier, but grouse are still the most challenging hunt.
We grouse hunters measure success in number of flushes, not by grouse actually taken.