Endurance means tolerating delayed evidence.

Evidence in long work arrives late, well after the decisions that produced it. That means you must act for extended periods on reasoning rather than confirmation, which is uncomfortable and is the actual difficulty of anything long-term. The silence is not a sign that you were wrong.

Decide in advance how long you will go without evidence before reconsidering. Naming the period beforehand protects you from re-deciding every time the quiet gets uncomfortable, which is when the worst decisions get made.