Thank you Mayben, E.J.H. and P.Barrie for your comments.
P.Barrie, your right: they are lots of learning, exhausting but huge learning. I did total 30 of them in January and suddenly in February I was in another daily painting challenge but that lasts only this week. It's a 7-day-challenge. But I couldn't say 'no' for it b/c they are my friends. So I keep painting dailies.