...we rejoin Patanjali's Yoga Sutra at sutra 1.30:
"These obstacles are disease, inertia, doubt, heedlessness, laziness, indiscipline of the senses, erroneous views, lack of perseverance, and backsliding."
-translation by B.K.S. Iyengar
My personal nemesis is inertia, probably followed closely behind by doubt. The hardest part of anything for me, yoga practice included, is just getting started. Once I do get started, self-doubts are often not far behind. I remedy this by setting aside time with my yoga teacher and with practice groups whenever I can. A nudge in the right direction from my teacher or a friend can definitely go a long way to help me keep the practice momentum going.