The ebb and flow of D/s growth is really quite fascinating.
male subs tend to foray into this lifestyle with years of developed fantasy and fetishes under their belt while Dommes often progress more slowly, dabbling in roleplay and gradually dialing up the intensity as her confidence grows.
The Dommes I have known over the years have often had a lot of fear inhibiting them during their developmental stages. This was often due to experiences with selfish subs that attempt to top from the bottom and/or refuse to participate in activities that aren't part of their fantasies. I think from a psychological standpoint it's easier for novice subs to embrace their role since many submissive characteristics are often positive for fostering relationships: being attentive to your partner's needs, making personal sacrifices for her happiness, giving up control to a stronger will, etc. On the other hand, novice Dommes are often haunted by dominant characteristics that appear negative out of context: being demanding, self-centered desires, cruel, etc.
Basically, it's harder for a Domme to be comfortable with her place in a D/s relationship than a sub. Early in, a sub is more likely to think, "this gets me off so I'm okay with it," while the Domme may be trapped by thoughts closer to "It gets me off to be horrible to another person, I must be fucked up." This is why it is crucial for fledgling Dommes to have early positive experiences in D/s or her confidence may be badly hurt and her desires buried. It's tough for her to feel dominant when she's afraid of making mistakes and unsure of how to go about things.
A sub will hit their confidence plateau early. If they can meet their Domme's sexual and D/s needs, the sub will feel comfortable and confident and there's a good chance that their interactions will at least somewhat resemble the sub's fantasies. A Domme will hit their confidence plateau much later on. It will probably take years of successful interaction with consistent sub(s) while developing new physical and psychological skill sets that allow her to feel natural in her role.
This is where the paths diverge most significantly. For Dommes, this plateau is very temporary and serves as a launching pad for her growth. She knows she deserves to get what she wants, she is confident in how to go about it, she may stumble here and there but understands this is part of the process. It is now where she can recognize her dominant hunger and is comfortable feeding it, confident in her sub's devotion and her ability to make things happen. From here she starts to press onward, following ideas and inspiration that may have piqued her curiosity or turned her on thinking about it.
A sub will usually roll with many of the new ideas she wishes to introduce as new and unexplored territory can be exciting for both parties. However, it is almost inevitable that eventually something will be introduced that will cause a drastic change and tear the sub from their comfort zone. They change the rules of the game. If it is part of the sub's fantasy, the sub will jump right in. If it is something the sub deems unpleasant, the sub will channel their inner used car salesman and spew a mountain of bullshit, explaining how it's better for the relationship to avoid doing it. Even introducing the idea will rattle his confidence and fear and doubt will cloud his psyche.
If the basics of BDSM are bondage and spankings, these new events are usually more psychologically intense requiring greater levels of submission and dominance to sustain them. Some examples might include chastity, cuckolding, branding, piercing, TPE, forced feminization, etc.
At this point, if the Domme caves to the sub's wishes without even giving it a try, that likely signifies the end of her dominant growth and the dynamic will remain stagnant for the duration of the relationship.
If she forces her will upon him or is able to convince him to give it a try, her growth will likely never stop. An event of this nature signifies the first time that the sub's will is truly broken. This firmly establishes a Domme's confidence and makes it more likely she will escalate the intensity over time. Also, once his will has been broken, it will be more easily broken again and again until he no longer offers any resistance to "game changing" activities or dynamics.
Once the sub's will has been completely broken, his confidence returns since his confidence will be solely based around his ability to please her and he will find him adaptable enough to please her in nearly any situation. At this point, the sub has basically given the green light for whatever she might wish for.
As a Domme realizes this, it may rattle her a little bit. I believe (although I could be mistaken) that many Dommes place a bit of a limiter on themselves when it comes to D/s, that is, there's a separation in what they WOULD do vs. what they SHOULD do based upon the sub's feelings. When that limiter is removed, she is the only one who can police her own actions and for the first time in a while she may doubt herself again, e.g. if something happens that can seriously damage the relationship, it's all her fault.
I believe this fear should exist, albeit being a little bit unfair as it's a rather heavy burden to carry, but it is something that should be respected in any case. I fully believe that for a relationship that has reached this point, the Domme will be very aware of the handful of actions that would probably damage the sub beyond repair and be able to steer clear of those actions.
On the flip side, I think the depth of a sub's love towards the Domme that has broken him is very great. 99% of the time, he will easily forgive her if something goes well beyond his limits. The remaining 1% are probably limited to those handful of actions the Domme is aware of and have likely been talked about since early on in the relationship.