What is Santosha? And how it helps me stick with yoga!

Why do I stick with yoga? I often feel like a shit in class, but unless I walk out injured, I always feel better at the end of a session.
One of my favourite teachers explained this feeling as Santosha: 'the sensation of stillness and contentment'. I don’t feel it often in life, but I do get a brief taste of it after class sometimes and it keeps me coming back for more!
It's a start and I’ll take it thanks.
Om.......