The Peter Principle was coined by Lawrence Peters in the 1960s, and states that in any organizations people rise to the level of their incompetence. Before they reach this point, they are performing effectively (exceeding expectations), and will tend to get promoted. Once they rise to their natural level of incompetence, they will no longer be seen as performing above expectations, and promotions come to an end.
Peter's book is very funny (if breathtakingly cynical), and entirely true.
Sometimes this principle becomes deadly. John Bell Hood was perhaps the Confederacy's finest Brigade and Division commander. Bold and fearless, he could be relied on to press the attack, literally saving the Confederacy in the Seven Days Battle outside Richmond in 1862, and breaking the Union lines at Second Bull Run. Hood's division saved Stonewall Jackson's Corps at Antietam, albeit at a terrible cost to his command.
Bold and fearless tactics garnered him repeated promotions, from Captain straight to Colonel, then Brigadier, Maj. General, and then Lt. General. The last was after the battle of Chickamauga, where Hood led the assault that broke the Union lines. Very much a "lead from the front" commander, Hood was wounded so severely that when his leg was amputated, the doctor sent the leg in the ambulance with Hood, assuming that Hood would be buried with his leg.
But Hood was tough as well as bold and fearless, and survived to assume command of the Army of Tennessee when Jeff Davis relieved Joe Johnston of command. Johnston had fought a journeyman retreat from Chattanooga in the face of greatly superior Union forces under Billy Sherman. In two months, Johnston had managed to keep his army intact in the face of dancing flanking moves by Sherman. And despite inflicting very heavy casualties on the Yankees, he'd been backed up against the defenses of Atlanta.
What Johnston knew - as did Sherman - was that the prize wasn't the city, it was the Army. As long as the army was intact and a cohesive fighting force, Sherman had to be careful. Jeff Davis didn't understand that, and when he replaced Johnston with Hood, he discovered that Hood had risen to the level of his incompetence.
In a month, Hood had broken the Army of Tennessee, cutting its strength to half what it had been at the beginning of the campaign. Frontal assaults like those at Peachtree Creek and Jonesborough failed to break the Union lines like at Second Bull Run or Chickamauga. Hood was forced to evacuate Atlanta.
He still hadn't learned. Trying to draw Sherman back north, he boldly invaded Tennessee in a lunge towards Nashville. Sherman didn't take the bait, and when The Union army closed with Hood at Franklin, Hood once more had his soldiers charge the enemy in what has been called the "Pickett's Charge of the West".
Bold, fearless, and - one last time - decisive. Sadly for Hood, the "decisive" part was his army essentially disintegrating under the pounding from Schofield's Federals.
Hood, you see, only knew one trick: bold and fearless assault. It carried the day a number of times, and he kept repeating the same trick as he was promoted through the ranks. However, Peter's Principle would not be gainsaid: once he rose to the level of his incompetence, he only knew his one trick. The tragedy of John Bell Hood was that once in command, in six months he destroyed what was left of the Confederacy.