Most important thing for Americans able to takes losses/pain is not only about losses of troops and equipment. The US is pretty much the only country when it fights the enemy, the enemy takes losses of troops and their own infrastructure, civilians, industry etc while the US only has to take troops/equipment losses. The US never had to worry about their own country, cities, infrastructure, civilians and industry to be affected. This is the single biggest advantage the US has which is why they can start war after war and their people not strongly opposing it.