The recurring wartime need for mass and reserves

What lesson does the world repeatedly fail to learn from major wars?

Advanced equipment does not remove the need for mass, depth, and trained reserve formations.

The answer warns against assuming a technological edge will remain decisive across an entire war. Opponents usually possess comparable technology overall, even when each side leads in different areas. High-end systems can improve effectiveness, but losses, maintenance, geography, and simultaneous commitments still consume force capacity. Mass and reserve formations provide the depth needed to absorb those demands. The lesson is not to reject advanced equipment, but to avoid purchasing it in a force structure too small to endure sustained conflict.