We couldn't improve in any area without resistance to what we are trying to achieve. It's that push, that brute force, that makes us stronger.
In martial arts theory, we see an enemy not as an enemy, but as a chance to perfect ourselves. So if we get hit, the response is NOT - "I hate him"- but rather "why couldn't I block it? Could you please throw that punch again - I want to see if I can block it this time". Without a yetzer hara, life would be meaningless.
I have discovered 3 things that I finally understand and would like to share with you.
1 - If we listen to Rebbe Nachman and live only this moment to its fullest, then a week or a month or even a year are all the same, because you are only living one day and dealing with its challenges. Tomorrow doesn't exist. As soon as you think "I am not certain I can last that long", that is SITRA ACHRA!!!
2 - A person only sins if a RUACH SHTUT enters him. I saw that this is really literal recently when I was close to falling, in that I was willing to take a chance on a full year's worth of work, my wife's faith in me, and the despair that would obviously follow the sin.
It finally makes sense how the Y"H gets his foot in the door, he makes you think that whatever you see now as a reality is the only reality, and that it will last forever. People commit suicide over monetary matters that any person with eyes in his head knows how it comes and goes.
I think that the RUACH SHTUT (that Chaza"l refer to) is that a person loses sight of everything important to him, and instead sees only the "now" and thinks that is all he can act on. Like if someone thinks "I have no money now, and this will be forever", then he will despair and seek an outlet for his despair and frustration. And we all know which outlet the Y"H wants him to use.
3 - Read "The Garden of Peace" by Rav Shalom Arush (translated by Rav Brody) if you can. It puts the role of the husband in a totally different light than you have ever seen. It doesn't really talk about sexuality, but anyone with eyes in their head will realize just how warped the modern view of sex really is.
I also heard this lecture by Rav Moshe New from Chabad.org which helped me understand what a woman really is on a spiritual level (here is the link).
Also, with you guys here, I feel I am able to draw coach from you even though we have never met.