I've had a few" landmark moments" with my dad over the years. A lot of my experiences growing up with him were not positive. I think the most important thing I learned about him was that he wasn't a bad person. He genuinely wanted to do the right thing. He was (and to some extent still is) a broken man who's own father completely destroyed him. That realization made it easier for me to forgive him and work towards repairing our relationship.
The most important thing I learned from him was that anger is a cancer. If you can't learn to let it go, it will metastasize. It rots you away from the inside out; physically, mentally, and spiritually. Robbing you of joy and cutting you off from the people you love while doing nothing to resolve the things you're angry about.
I am extremely thankful that I learned that lesson at a relatively young age and before I had kids of my own. By the time my dad figured it out the damage was already done.