Sometimes, when I'm struggling with playing something at a given soft dynamic, I make myself remember that dynamics are relational and not absolute. So I practice it a more comfortable dynamic, while sounding the notes the way I'd want them to sound were they at the dynamic level I'm aiming for (for example, with a more prominent upper note, often with a subtly voiced bass note, depending on the music), so I'm doing everything how I want it to be but maybe at MP rather than PP. This fixes the tone-to-tone relationships and voicing I want, and it's obvious that it's mechanically possible for me to do. Then I look at the surrounding music. I tend to play delicately, so it's often the case that right before the dynamic change down to PP I'm already playing pretty quietly, which makes for more of a strain to play even more softly for what's notated as softer. My teacher says, and this is brusque paraphrasing, that dynamic levels are more like the general vibe of what's happening instead of something like a fixed and objective decibel readout. So when it's time to go quiet, if what comes before and after are distinctly not as hushed, even something played just kinda lightly (with the more prominent notes not all that light in reality) will feel much lighter. So instead of taking the microscope to a single chord that you're having issues with, you might be able to look at the passage in question more holistically in order to ensure that there's contrast there. And maybe it's not your platonic ideal for the sound in that one particular spot, as a whole the passage might sound smoother and more coherent. Then you can flag the passage as something you would like to work on over a longer term, somewhat content that you can make it sound musical at present, even if you want it to be special or particular in the long run. To me one of the most difficult skills at the piano is playing with nuance and consistency at very low dynamic levels. It's easy to be hyper-focused on this and to become discouraged or overly fixated, but it's important to remember than music is organic, that it's not just a matter of lapidary details but how things relate to each other. Sometimes what is PP in one section might be the same, volume-wise or amplitude-wise, to MP or just normal playing, in another section, the difference being mostly in how it relates to what comes before and after and how you lead the voices or figurations in the piece.