I often wonder about personality styles tossed into the mix, plus the extra friction oldest to second. When it's good it's good, but when it's bad it's really bad. Your post made me think about my second born pulling me in next to him for a family photo at a baseball game, the other night.
I'm an only so this birth order thing, I find fascinating.

Maybe it's irritation with your siblings that came flooding back? Them getting attention resembled the past?

Let me clarify, attention. Not in an envious way for a middle child view, but darnit my parents still need to tiptoe around their emotions type of attention?

"Investigate your hidden assumptions."-Cornel West