How do you balance accepting the unpredictability of life with taking responsibility for your decisions and actions?

I hold two contradictory ideas in my hands loosely. I act as if my decisions and actions matter, because for all I know, they do, and I have to act as if they do, because I don't want to be a passive bystander, I want to believe that my actions effect the world, and I actually know that they do effect the world because I've experienced how me doing something changes things in the real world. But I also know that my actions are just ripples in pond with innumerable other ripples interacting in this dance that I can't see fully, and there are forces acting upon my life that I have no control over and despite my best decisions and actions, there are things simply out of my control, and I have to be okay with that as well.