There can be many hard things about a yoga class. Perhaps what comes to mind is a physically difficult pose like (insert your hardest pose(s) here) or a relaxation pose like Savasana. But I think and will often say the hardest part about yoga (asana) is the act of showing up. This is true whether you are physically showing up for a class or mentally/emotionally showing up for yourself while on your mat (at home or in a class). The cool thing about yoga is that it doesn't care how often you practice or whether you can do a "hard" pose or not. It just cares that you showed up. (And you don't even have to show up happy. You can show up grumpy! How great is that?) And another cool thing about yoga is that once you practice showing up on your mat, it makes it that much easier to show up off your mat. As in--show up for your life, show up for other people...
But, I do indeed find it hard to wiggle my fingers and toes after a deep, restful savasana.