Even though I think he intended this to be rhetorical, it's a fundamental question that deserves careful attention. To make an impact it's best to avoid the big errors, the ones that drain our energy in fixing and cleaning up the consequences.
Many would cite poor decisions, bad luck, lack of information, emotions, being mislead, rushing etc. as reasons for our snafus. All are valid, but are there some deeper causes that lead to our propensity to mess up? One answer comes from the discipline of systems thinking which shows that often, no matter how good our intentions, we end up making the wrong long-term choices and creating problems because we fail to see the underlying systems that dictate outcomes. When something appears broken we have a natural inclination to take it apart and fix it, applying solutions that mend the broken item or issue. The systems thinking idiom is that you cannot mend the system by fixing the parts; you must begin with the system in mind, and act to benefit the system goals. A classic example is the climate change conundrum, where current paradigms constrain us to continually contribute to a problem that will eventually make life on the planet untenable. Even when we see the system it is not easy to change the underlying structures.
Being able to visualize dynamic complexity--interrelationships when all variables are constantly in flux--is not trivial and requires considerable computing power. Nevertheless, it is powerful to just shift our mindset and appreciate the extent to which everything is interconnected, understanding that changes in one area lead to results that are separated in time and space. Our lives and their impact on the world represent our principal system of concern. When we begin to discern how choices and actions affect others and subsequently feedback on our own lives, we begin to see different strategies to make the most impact. There are true points of leverage (and I don't mean "leverage" in the corporate jargon sense*). We can construct a means of really learning from our mistakes by using them to understand interrelationships, and the mental models that we used in the situation [Got Impact Models]. Seeing these structures and models ever more clearly is the path to continual learning and impact.
Cause and effect is rarely unilateral and linear; effects may be distant in time and location from their cause. As of writing this post, the current Isis insurgency in Iraq is a good example of a core concept in this systems worldview: "today's problem is yesterday's solution".
Don't be fooled, look at every step in the context of the larger journey, strive to understand your mental models and the structures that govern cause and effect. Learn, integrate and test; understand that sometimes the fuck-ups that occur are the result of the system, and the better you understand the system (and challenge it, redesign it, change it!) the better you will be able to answer Neil Young's question.
*"we can leverage that Jim"