Dd1 was just getting to that stage where she wanted out of the buggy, so I started with small trips, like to the shops 10 minutes away.
She was good, holding hands all the way there & most of the way back. When we stopped at a crossing on the busy road, she must have decided she didn't want to stop, because she slipped my hand & ran.
Right into the path of a oncoming truck, with a driver staring out of his window & whistling at some young girl on the other side of the road, one so he didn't see her (no one had respect for this crossing, as it wasn't one with lights, you just hope that the drivers stop)
As a mother, your instinct is to protect your child....but I could not move. I was rooted to the spot. I screamed tho...which alerted the driver who braked as hard as he could. Inches from my dd.
I decided not to use reins that day, as she had proved she could be 'trust worthy' and that she 'understood the concept' of not letting go of my hand & had NEVER ever bolted before. I still get a feeling of nausea as I write this, almost 4yrs on.
It only takes one time. Yours was in a supermarket, mine was on a road, with real dangers. I guess that is why I love reins & didn't trust my daughter 'getting the concept' for some time after that.
YOU have to learn some lessons, sometimes...as well as your child.