Why combat units need rotation before collapse

Can a person normally endure about 200 days of combat before needing relief?

That is far too long; troops need rotation much sooner to avoid emotional and physical collapse.

Two hundred days is rejected as a realistic average limit for continuous combat. Personnel need rotation much sooner to avoid emotional and physical collapse. The three-day French model at Verdun mentioned in chat is treated as plausible within a wider rotation across the front. Endurance depended on a system of relief and replacement rather than an individual's toughness alone.