"I'm not flexible enough"
It's the single most common reason people give for avoiding yoga altogether, the assumption that you need to already be flexible to get anything out of it. Richard, who teaches yoga alongside his acupuncture work, spends a fair amount of his second Yoga Magazine column dismantling that idea, because it puts people off a practice that was never really about the shape you can bend into.
Compression, not just flexibility
A lot of what limits someone's range in a posture has nothing to do with flexibility at all, it comes down to compression points, the simple mechanics of individual skeletal structure. No amount of willingness will move bone past where bone physically stops, and pushing beyond that point is how people get hurt. On the flip side, being naturally very flexible, even hypermobile, doesn't automatically mean someone's getting more out of a pose, or achieving some deeper "correct" version of it.
The real common denominator
Richard's own view is that yoga is really about the absence of tension, not the presence of flexibility, moving within your own particular structure, but doing it without unnecessary strain. As an acupuncturist, he also points out that tightly contracting muscles to force a posture can actually blunt its effect, since it's the gentler activation of connective tissue, not brute effort, that stimulates the corresponding organs and systems in the body. Relaxing into a pose tends to do more than pushing through it.
What it's actually practice for
Ultimately, Richard frames the mat as a kind of laboratory, a place to practise unconditional acceptance of your own particular shape, rather than comparison with anyone else's. That's a mindset that tends to travel well off the mat too, into how readily you can extend the same acceptance to the people around you.