The remark treats trust as a practical decision rather than a vague feeling. When people depend closely on one another, partial confidence may be insufficient: each person must judge whether others are reliable enough to be entrusted with important responsibilities. The emphasis therefore falls not only on trust itself, but on the judgement required before granting it.

In For Whom the Bell Tolls, Robert Jordan operates in circumstances where mistakes, betrayal or hesitation can have severe consequences. His mission depends on co-operation with people whose motives and reliability he must assess quickly. The quotation reflects the difficulty of making such decisions when complete information is unavailable. More broadly, it applies to teams working under pressure, where effective collaboration depends on confidence that others will fulfil their roles. Hemingway’s formulation also recognises the risk involved: trusting someone requires a decision, and that decision may later prove either justified or mistaken.