For an armed forces commander, for a tackle football coach, for a trial lawyer there is a meaningful sense in which the main actor has to react rather than act, let events take the course they will and adjust. Adjust. If you follow your war, game or trial plan without adjustment to developments in the arena you will lose as surely as you would had you not prepared at all. I think this is missing from war histories, Monday morning quarterbacking, and trial autopsies. 

Abraham Lincoln and the United American people were befogged from the outset of the Civil War, not clear even in their own minds if it was a war, if it was what it was about, and with no experience, no idea really, how to fight a war. It was all seat of the pants and it had to be all seat of the pants. McClellan made the most perfect plans, his army was immense and shiny and spiffy but McClellan would not fight. His predecessor, General Scott, had a grand plan, the "boa constrictor," to slowly but surely suffocate the Confederacy. Halleck, McClellan's successor, had a plan: take territory, Confederate towns and cities, critical crossing points, all the better if the enemy simply abandoned the targets with no loss of life. Initially President Lincoln was of the same mind as each of his three commanding generals. He did not want a war of conquest of the Confederate people, civilian life was to be spared, private property unmolested or if appropriated unavoidably, receipted for reimbursement. To avoid war Lincoln would have kept all the slaves enchained, freed some but not others, or freed all. Whatever would have worked. Lincoln did not grasp initially that to win the war slavery had to be killed dead. He would learn. In the Spring of 1862 Lincoln also learned that his armies were a terrible sword only if wielded, and wielded swiftly.

Lincoln...came to see something which he never forgot. The Southern Confederacy lived by its armies. While they lasted it would last and if they died it would die...(Catton, Terrible Swift Sword 303)

The Confederate army must be destroyed. Lincoln was learning as events took their course, he was reacting, adjusting, changing, both his thinking and the use of his armies. On January 1, 1863 he issued the Emancipation Proclamation, having learned that slavery must be destroyed. And in 1864 he came to see that "South Carolina must be destroyed". That is, Lincoln learned that this was a war between peoples, not just between armies, and that Confederate civilians and all that they owned or possessed must be destroyed. 

Some historians fault Lincoln, although the generals take the overwhelming share of the blame, for being irresolute. Monday morning quarterbacking. The United people in 1861 and 1862 were not ready for the war that the Civil War would become, not a war between peoples, and the president could not get ahead of the people. Once begun a war or a football game or a jury trial becomes almost a living thing itself and the main actors ride the crest and adjust, cutting a channel for the current here, going for the blocked punt there, deciding that your client will or will not testify. Sometimes decisions that a few months or moments ago were unthinkable are made and they are the right ones and they are made by the people. Sometimes the people decide to abandon Moscow with Napoleon approaching. These are decisions that can only be made and are only made when they have to be made, that is, when events force decision. You can plan till all hours of the morning before a trial begins, but if you stick to your plan come hell or high water you're not being resolute you're being bull-headed, you're blindly following your own road map and not paying attention to changes in the terrain. And you'll catch hell.