I'd really like to hear what people have to say about this. To me it's very powerful. It says a lot about the meaning of this struggle.
One idea I think about alot, that is relevant also when there are less nisyonos, on the subject of Yesod, is like this: when I have a desire to act out it is usually when I feel I want to escape. My life is just not interesting enough, or things are not going my way. Deep down I feel there is something great about me, that I have so much potential, but the world I am in doesn't reflect that. People don't appreciate me, or I am not succeeding, or not succeeding enough, or I don't feel satisfied enough by my success. In the imaginary world of P&M, everyone loves me, I can always get my way, there are no limitations, and I get a huge rush of excitement and momentary validation.
The Middah of Yesod is to be able to focus all of our energies on specifically the reality that we are currently faced with. Before they build a building they dig a foundation, they prepare and designate this specific place to build, and not somewhere else. We live in very challenging times. Because there is so much Tumah in the air, and our society's values are so crumbled, it is difficult to learn, to connect. We may tend to feel that it is just not working. We heard so many lofty things about the Torah, about Tzadikim, and we just don't see how the reality in front of us is supposed to be the opportunity to connect to those things, and to bring out our potential. But we have to know that when we commit to putting everything we have into the reality in front of us, we are accomplishing much more than we can even understand.
That is what blows my mind about the Nisayon of Yosef Hatzadik. He was sold as a slave, betrayed, tested day after day, we all know the story. Let alone the Taiva that was involved in his test, but how was he even able to muster up the strength. What did the reality infront of him have anything to do with the legacy of Yaakov Avinu, of those great things? If I was there I would have felt, who even cares what I do anyway?
That is Yesod. It is not only applicable to shmiras Habris (even though it is most applicable there). Just like a person should focus all his energies on his wife, a person should focus all his energies on everything he does, to bring out the most kedusha possible.
This is also part of הלכתה בדרכיו. Hashem has literally limitless goodness and greatness to reveal and shower upon us, and He creates a specific place, a specific כלי to shower it there. And then miraculously the כלי is able to hold, to reveal so much more than it's own limitations. Kind of like the Aaron that was larger than the space it was kept in. Or the way the Beis Hamikdash was able to hold so many people at once, and everyone was miraculously able to lay down and prostrate on the floor without climbing on top of each other.