I think this is a great question, but probably doesn't have a universal answer, though we likely all have commonalities. i get that there are some Dom's or subs who only consider D/s 'true' if the Dom chooses. But for me, and other Dom's or subs i have known, a big part of D/s is the Dom figuring out the keys to evoking deep submission from Their sub... i.e., submission is not assumed or automatic, it's discovered and exploited. So, i think asking questions like this is apropos.
For me, D/s is psychological at its root. Too simply put, it's about wiring and the Dom's need/desire to control and the subs need/desire to be controlled, to submit.
Personally, my sub isn't elicited by force or bullying. Probably one of the most profound experiences i ever had with a Dom was sucking His large cock. He forever changed me in that area. Prior, i didn't have all that much interest in sucking. Sure, i'd do it because i love to please guys, but i'd rather get fucked and bred. But He wanted me to suck Him. He was about 8.5" and very girthy, He sat against my head board on the bed with His legs opened and had me lie between them on my stomach... it was an awkward position. He took the attitude of a coach with a kid. He did nothing but encourage me and when i did something He liked, He'd gush "GOOD BOY!!" and heap praise on me, like i'd just done something heroic. As i was trying to take Him, He'd coach and encourage; "that's right, just a little more, just around the curve...." He kept directing me to look up at Him, and He'd lock onto my eyes. He'd ask me questions like ", you're doing so well, aren't you so proud?" knowing i couldn't talk with my mouth full, but fully expecting an answer and i could only mumble. my nose started to run and my eyes got teary, i kept gagging and He just kept praising me and telling me what a "Good Boy!!" i was. That was embarrassing for me. i think what was most embarrassing was how proud i felt about pleasing Him and how good i would feel when He called me a good boy and told me how proud He was of me. i felt humiliated and embarrassed and at the same time, adored Him.
He completely opened me and had access to me. It was an amazingly deep connection. that's what i look for with a Guy.