"Set out" means to start a journey or begin an activity with a specific goal in mind. It's like when you pack your bags and head out on a road trip, or when you start a new project at work. "We set out on a road trip to the coast." "They set out to build a new house." "In retrospect" means looking back on something and thinking about it differently now. It's pretty common in everyday talk. You might say, "In retrospect, I should have studied more for that test," or "In retrospect, moving to this city was the best decision I ever made." Here's another one: "In retrospect, I should have taken that job offer." And one more: "In retrospect, we probably shouldn't have bought that car."