I never really liked onions, mainly because my preference to avoid them was taken advantage of when I was a child. Whether it was onions or black pepper (and now, I enjoy black pepper), I was tormented by an adult relative for my choice.
-- Fortunately, that phase is over with. But there is something about onions that is really useful when dealing with the changes that occur in the learning process. Learning by your emotions, learning by your body, learning by the book, learning through experience -- .

As you learn, you become a changed being in navigating through life. I wish that all learning were positive. When we learn to distrust our fellow creatures and human beings, it is a challenging issue to regain a feeling of safety, security and openness. Will you stop, mid-way, and stop peeling the onion, because of the slight irritation to nose, throat, and skin? Or do you keep going, knowing that onion provides an essential element to the culinary process?

Do we give up on our fitness goals because of "peeling the onion"? Yes, there is some physical irritation in the process; maybe even accident or injury. But give up?
How about the quote of Edison: "I have discovered the multiple ways that don't work (to discover the electric light bulb)"? Is your body aching more than when you started your routine? That's the "peel the onion" effect. You may have made an overuse or lack of awareness error in your exercise choice and attention to form of holding your body; you just might not have been ready to take on the next step.

And you may not have injured yourself. Instead, you might actually notice how tight or sensitive your muscles are -- because now you have the awareness to notice such things. Whatever your variety of onion - figurative or literal - give yourself the opportunity to discover its message for your practice.