When I find it hard to forgive myself for all the past decisions gone awry I remind myself that every decision I've made was the correct one at the time.
Consider this, when you make a decision you must gather facts and weigh your options using the mental model embedded in your head. After letting all these inputs stew together with your emotional state of mind, you make a choice. As long as you were well intentioned, you can rest knowing you did the best you could because there's no way to retroactively change the ingredients that have gone into a decision that's already made. In other words, you're never wrong.