On this date, in 1815, Napoleon Bonaparte, the greatest general of his age squared off against an array of troops, mostly British, under the command of the Duke of Wellington, at Waterloo, Belgium. The battle started late. It had rained the day before, and the ground was initially too soft to allow firing of the French artillery. But with some 90,000 troops, Napoleon thought the odds were high he'd win the battle.
Up to that point, things had gone pretty much as the French Emperor planned. A surprise move to Charlerois, an attack on a Prussian army at Ligny had driven both Allied Armies back. More importantly Bonaparte had split then. Sending his newest Marshal, Grouchy, with 60,000 men after the Prussians, Bonaparte pursued the British. The only flies in the ointment were the unnecessary delay the French took against the British at Quatre Bras, and Grouchy's too literally following the Prussians, instead of screening Napoleon's right. But the seeds for disaster were now there.
Napoleon was lethargic on the day of battle. It appears he was ill, and remained at his headquarters, leaving the conduct of the battle to Marshal Ney. A man of almost foolhardy bravery, but limited skill, Ney, by late afternoon had frittered away most of his infantry, destroyed most of the cavalry, and faced the Prussian Army coming in from his right, with the British still to his front. At the point, Napoleon committed the OldGuard, and as the saying went, "Le Garde recule".
What lessons are there to be learned from all this?
 Choose your subordinates carefully. Bonaparte miscast most of his major players at Waterloo. Soult, one of his best field commanders was stuck as his chief of staff, a job for which he ill-suited. Davout was in charge of Paris. Murat was not employed at all. Ney had never commanded more than a Corps, and was not well constituted for independent strategic action. Grouchy had never commanded more than the Guard Cavalry, and literally followed the Prussian line of march. Even when he heard the sound of battle to his west, he didn't head to the sound of the guns. The Prussians wound up between him and his Emperor.
 Grow with the times. The British countered the French infantry tactics with a double line of infantry defending, initially, from behind the reverse slope. This both negatived the Grande Batterie artillery tactics Napoleon favored, but also allowed the Brits to cover a longer front with less men. The French, whose tactics had not changed since Royalist times, attacked in Battalion columns. Easy to control. Easier to shoot.
 Show flexibility. Bonaparte's command system did not encourage independent subordinates. With the exception of Massena, Soult, Davout , and Surier, most of Napoleon's Marshals did not flourish out of his sight. When he was down at Waterloo, for whatever reason, this lack of independent subordinates killed his chances of winning, which leads to:
 Develop your subordinates. Napoleon never did, beyond the point of supervised Corps. command. Develop your tactical systems, your weapons, and your organization. All of the French artillery were designs going back to the Royalist army. Ditto the infantry weapons. Napoleon's only contributions to French military might were the Corps system, and the use of heavy cavalry. He refused to develop rifles to replace muskets, loosen up infantry formations, or change his methodology. As Wellington said, "They came at us the same old way, we beat them the same old way."
Waterloo is now some 199 years in the rear view mirror, but a lot of what Bonaparte should have learned, is applicable to most endeavors, not just war, today. And if he'd learned them "Waterloo" might well be associated with Napoleon's name in an entirely different way today.