Understanding skill versus luck in performance outcomes is critical for long-term investing success. After adjusting for risk and considering costs, most serious studies have concluded fund managers outperform due mainly to luck. See:

Eugene Fama’s and Kenneth French’s 2009 paper, “Luck Versus Skill in the Cross Section of Mutual Fund Returns” which demonstrated that “the high costs of active management show up intact as lower returns to investors.”

Regarding “all of the news [you] had digested and interpreted,” the real understanding is assessing whether any of the news is not already reflected in prices. In highly competitive markets very little news is not already digested. When an investor thinks they have an edge, they should ask whether the institution on the other side of the trade has better information and analysis. My preference is to focus on diversification, taxes and risk premiums while keeping overconfidence, hindsight bias, and other factors in the behavioral finance realm in check.