The time to worry is three months before a flight. Decide then whether or not the goal is worth the risks involved. If it is, stop worrying. To worry is to add another hazard. It retards reactions, makes one unfit. Hamlet would have been a bad aviator. He worried too much.
Earhart distinguishes useful preparation from unproductive worry. Before a demanding flight, she argues, the risks should be examined carefully and the value of the goal should be judged against them. That is the appropriate stage for doubt and reconsideration. Once a considered decision has been made, however, continued worry offers no practical benefit and may interfere with the concentration needed to act safely.
Her point is therefore not that risk should be ignored, but that concern should serve decision-making rather than persist indefinitely. Earhart links excessive worry with slower reactions and reduced effectiveness, making emotional control part of practical competence. Her reference to Hamlet adds a literary example of prolonged hesitation: his tendency to deliberate and worry contrasts with the decisiveness required of an aviator. More broadly, the passage advocates careful judgement before commitment and composure once action has begun.