If you know the ancient writers, you must be puzzled why moderns often pronounce that ancient Greek armies were highly skilled and rigorously disciplined. Those writers make it clear that getting high-status Greek men to accept any kind of training and discipline was like getting them to pick a day to have a tooth pulled. Spartans accepted commands and corporal punishment and did a bit of drill, but no ancient writer describes them practising marching or fighting in peacetime. One reason why people say things which are contradicted by so many ancient texts is that they are using the ancient Greeks as an excuse to talk about their own culture, so they project things they love or fear about their own culture on the ancients.
Have a look at this quote from Professor Emeritus, Colonel (retired), Dr. Jonathan House who is talking about how the proud professionals of the German army got themselves spanked by the Red Army.
Germany, in fact, is the poster child for what we like to call the Western Way of War, the idea that a well-trained force can achieve rapid offensive decisive victory by superior discipline, manoeuvre, and equipment. Well, that works part of the time, but if you encounter somebody who is not willing to say he’s defeated, as the Soviets were not, and then you encounter somebody who in addition to that has all this vast terrain, then eventually your plan gets thwarted.Dr. Jonathan House, “How the Red Army Defeated Germany: The Three Alibis,” 2 May 2013 https://www.youtube.com/watch?v=zinPbUZUHDE 20:00