The idea is to do one's work without emotional attachment to "results". In modern day psychology it is called "self-distancing". It is nothing mystical but commonsense. The way to understand the rationale is; even though "self-effort" has to be put forth towards a goal, because there can be so many other factors involved in deciding the outcome (most important being random chance) that it is best to have no emotional ties to outcomes. That way one does not fall into despair and a negative frame of mind if things turn out wrong but still can choose to experience joy when things turn out well.