Endurance is distinct from strength. Strength is the capacity to meet a peak demand. Endurance is the capacity to continue meeting the ordinary demand after the peak has passed and the initial energy has been spent. The differentiated individual requires both, yet in a late age endurance is the rarer and more decisive quality. The forces of dissolution operate over long periods. They do not require dramatic opposition. They require only that the man eventually yield.
The age trains the young man for short intensities followed by recovery and novelty. That training produces men who can rise to an occasion and then collapse into the surrounding current. The higher type cultivates the ability to remain ordered across weeks and months of unremarkable pressure. The work is rarely dramatic. It is the continuation of the same standard when there is no external recognition and no immediate reward.
Young men often confuse endurance with stubbornness or with the refusal of rest. The distinction is clear. Stubbornness is rigid and eventually breaks. True endurance is flexible in method while remaining fixed in the measure. Rest is taken when required. The standard itself is not suspended. The man returns to the same line of action after the necessary recovery.
Build endurance in the domains already examined: the body, the speech, the attention, the small decisions. Do not seek extreme tests. Seek the capacity to continue the ordinary applications without interruption. That capacity is what allows the type to survive the full duration of the cycle.