Short answer: NO! Long answer: No, this is a stigma that often people think is true, when it is not. Flexible or not, is it not essential before trying out a class. BUT, when you continue to practice, you may notice that your body starts to become flexible over time. The reasoning with practicing yoga is for a better connection to the mind and body, not necessarily to be flexible. You can always take modifications if you cannot do a pose. The internet "picture" of yoga are those who are always flexible, you your pose does not need to looking nearly this like. It is all about how the pose feels like. Thank you for watching!