Look at her. She's just fallen on her face, trying to crawl but unable to coordinate her limbs properly, but she's not upset or frustrated. She's calm and interested, nothing more. It looks as though she just decided to take a quick break right there, and as soon as she's ready she'll be back at it. Which is, in fact, just what happened.
She's not always an angel, but she's so often so good-natured that I can't help but wonder where she gets it from. Not from me, certainly.
This photo was taken less than three weeks ago. She not only crawls well now, she's even started pulling herself up on the furniture. Still calm, interested, and happy, but I'm going to have to move a lot quicker now.