The Roman cursus honorum
This is documented history rather than a laboratory result. The events are well recorded. What they teach is an argument, and the entry makes it openly.
The Roman Republic had a fixed ladder of public offices called the cursus honorum, the course of honours. To reach the top, a man had to climb it in order, holding each office before he could stand for the next, and there were minimum ages written into law for each rung. Even the brilliant and well-connected were expected to climb it in order, and although powerful men sometimes won exemptions, the rule held for most of the Republic's history. To become a consul, the highest office, a man was meant to have served in the lesser roles beneath it first, gaining the experience each one demanded. The Romans built this deliberately, because they understood that the judgement required to hold real power was something formed by running smaller commands, making smaller decisions, and living with smaller consequences first. Seniority had to be earned in sequence, not granted.
The judgement a senior role requires is built by holding the roles beneath it, which is why dropping someone into a big job without the smaller ones underneath tends to fail in specific, predictable ways. A person given a senior title they have not grown into has skipped the very experiences that would have taught them how to hold it. This is worth remembering both in how you promote people and in how you judge impressive titles: a grand role reached too fast, without the layers of smaller judgement beneath it, often sits on a hollow foundation. What looks like bureaucratic obstruction is how the capacity to handle the top job actually gets made.
The failures have a recognisable shape. Someone promoted past the rungs cannot reliably tell good work from bad in the function they now oversee, so they fall back on judging confidence and presentation. They lean on the one skill that got them the job, because it is the only one they have tested. They misjudge how long work takes, having never done it at the level below. And they either escalate decisions they should be making themselves or avoid them entirely, because they have no earlier cases to reason from. Each of these gaps traces back to a particular experience that was skipped, which is why training added after the promotion rarely closes them.
The same failure, described as a general tendency rather than a Roman one, is the Peter Principle.
Rome made it impossible to reach the top without every rung, because the judgement the top job needs only forms by holding the smaller ones. The Mongols promoted a blacksmith's son with no military background straight to command, and he went on to win campaigns across Asia and Europe. Both worked. What separates them is what the role actually demands. Where the job is judging work in a function you have never done, the skipped rungs show up as predictable failures. Where it is producing results under stress that can be seen directly, pedigree only measures how someone was selected before, not what they can do now.
Source: Documented Roman history. The sequence was formalised in the Lex Villia Annalis, 180 BC, which set minimum ages for each office. An accessible history of the period: Mary Beard, SPQR, 2015.
Mary Beard, 2015
A clear-eyed history of Rome, including how it structured power and who was allowed to hold it.
The Saturday letters
Every Saturday, one idea worth your time, with an honest account of how far the evidence really goes and where it stops. Free, a few minutes to read, and it leaves you with questions rather than instructions.
Draw your own card. It does not take long, and it rewards taking your time.