Lady Grey's comments really got my mental gears turning on this. This is one of those cases where I feel like trying to understand the D/s dynamic and submissive response is buried under many complicated layers.
I've scraped the surface of this in the past and my tears post after Reflections covered it a bit.
If I had to describe my greatest submissive need, I would say it is subspace. Not the masochistic high that is sometimes described after pain or impact play, but straight up "mental bondage." I crave to be forced into the deep end of the pool. To sink into its depths and feel my ego die and persona shift catering entirely to her.
Unfortunately with subspace, our triggers eventually become ordinary. If we are no longer bothered by them to the same extent mentally/emotionally and if we have confidence in our abilities to endure and perform with those triggers present, they just don't sting in the same way. Our emotional capacity adapts. It requires something else to "get us there."
Now don't get me wrong, simple sets of rules, rituals, and behaviors are enough to push me into subspace and enjoy waiting on a woman hand and foot, pleasuring her, worshipping her, and loving her with my entire being. Here I am referring to that place where I mentally adhere to the ideas that she determines what is right or wrong, deserved or undeserved, and so on. This is the place where she truly becomes a Goddess.
Over the years I have noticed a few trends in dynamics that often get treated as being the same, when they are in fact a little bit different. Namely, there is a difference between doing something you don't want to do vs. doing something you have said you don't want to do.
An easy example of this is ordering a sub to wear panties. This will likely embarrass him a bit, make him self-conscious, and while wearing them, he is likely to be more docile and obedient. I believe the resulting change in behavior and attitude/demeanor are his mind coping with doing something he did not want to do. He didn't ask to wear panties, the choice was forced on him. He doesn't want to wear panties, but the thought of being disobedient is worse. While he accepts this rationally, it affects him internally, pushing him into a new form of subspace. At its root, I believe this is an example of what happens when you are forced to do something you do not want to do. The reasons may differ, avoiding punishment, wanting to please her, etc. but it does require coping.
There is a deeper level of this and I think this is what tends to "do it" for my subspace the most. Taking that same example, let's say that at the beginning of the relationship the sub stated outright that any type of feminization was a soft limit. That is, panties would be something they would not reject, but it is something they wished to avoid unless she REALLY wanted it or had a very good reason for it. If she orders him to wear panties under these terms, the sub has to deal with the same emotional hurdles as the previous example, but it's magnified by the fact that he overtly stated it was something he did not want.
From my experiences this forces the brain into an even more difficult position. "She knew I didn't want this and she did it anyways." This is fairly jarring emotionally. It stings worse than the previous case. It has a stronger effect on a sub and their space.
What can follow is also very critical in how this affects the sub. In most cases, I believe if a Domme chooses to push a sub past known soft limits, she will generally share a reason as to why (he may ask or she may share it openly). The reason given can dull or increase the sting. If she responds with "I wanted to increase the power of my dominance and the depth of your submission," or "I want you to be more docile," these are reasons that a submissive can process logically and agree with.
There are an entire spectrum of responses that reinforce the D/s dynamic and vary the intensity of feelings within a sub. The "better" the reason she provides, the easier it is to bear. The more the sub can use logic to agree to it, the less it will torture him inside.
"Because it amuses me." -> I bear with it because I would not want to deprive her pleasure.
"Because it's cute when you blush." -> I bear with it because it touches her and feeds her dominance.
"Because I like to see you squirm." -> I bear with it because it feeds her dominance.
At some point of increasing intensity we reach a line in the sand where it requires more emotional sacrifice to handle it.
"Because I felt like it."
"Because I can."
"Because I was bored."
"There is no reason."
As this continues we approach the final line in the sand. At this point a sub can no longer rationalize it.
"Because you don't want to do it."
"Because it makes you uncomfortable."
And at the very bottom lies: "I'm making you do this because I know that you hate it."
I can't think of a reason that would sting worse than this. This reason alone is enough to push things deep into subspace, no matter what the activity is, hell it could be eating badly prepared lima beans. It just leaves you feeling completely defeated.
Looking back upon why pegging is showing up in fs01 when I/he hates it... I think it's in order to live vicariously as I write and remember the feeling of my spirit being crushed as I endured something that was a hard limit of mine for 7 years. I hated it, it felt terrible, it made me feel terrible inside... but it also pushed me so far into the deep end that I felt... completely 100% owned.