So, back to stance, posture, and why it's so doggone important.
The way you present yourself speaks to the degree of seriousness that you have for the person in front of you, or the activity you are engaging with. Weak stance and posture isn't just incorrect; it reeks of disrespect. Hands on your hips or loosely balled up below your waist when you should be in "ready stance"? Really? Arms folded across your chest like you're bored? Those are a couple of common examples of poor stance and posture that I have observed during times of instruction.
It all boils down to respect. Present yourself correctly. Position your heart and mind to be in a place where you can honestly, humbly admit that everyone you interact with has something that they can teach you.