I've long known of the Japanese focus on Hara without understanding it well. I originally thought it mainly concerned developing an impregnable energy centre in the martial arts. Not so...
I've noticed lately when I get sucked into something and give it too much attention (or worry), it's helpful to re-centre by dropping my consciousness to my 'middle'. When I do that my shoulders drop, my breathing deepens and the mental frazzle dissipates. I can 'let go' and return to the present moment.
I was taught to start meditation with 'circular breathing': taking a few deep breaths while picturing a flow of breath-energy going up the spine, over the head and down the front. This, too, is settling into Hara.
Kodo Sawaki Roshi (pictured) emphasised doing zazen with the self settled into the Self... the self that extends through everything in the Universe . A strong sense of connection materialises when we drop our boundaries and settle into the Hara.
And Rindo Fujimoto Roshi's instruction to put the Mind in the left hand  is clarified when we notice where the hands rest when we sit in meditation.