Just as you had to learn to hold it in once upon a time, it takes some practice to consciously relax those little sphincter muscles. These days, when I'm wearing, my subconscious knows it can let go with only the slightest prompting from the aware part of my mind.
The thread brought back the memory of the first time I peed in front of someone (after toilet training!). Age 11 or 12, I had on a pair of my baby sisters plastic pants over as many underwear briefs as I could lay my hands on. with baggy pants and a shirt on over that. I let flow, intentionally, while talking to my mother in the basement laundry area. To the best of my knowledge, she had no clue, then or ever.