Succession is discussed as a planning exercise and determined by something earlier. A successor exists only if someone was previously permitted to make decisions of the same kind.
Readiness is produced by practice, not by identification
Naming a potential successor changes nothing about their capability. What develops the capability is exercising judgement on real decisions with real consequences.
That requires the incumbent to hand over decisions they could make better themselves, and to accept worse outcomes during the period of learning.
Leaders who retain the difficult decisions produce a bench that has been observed rather than tested, which is a much weaker basis for a transition.
The short-term cost falls on the incumbent
Delegating a consequential decision costs time in explanation and risks a worse result, both of which appear in the current period's performance.
The benefit appears years later and often after the incumbent has moved on, so the person bearing the cost is rarely the one who collects the return.
Any structure with that shape produces less delegation than the organisation needs, and succession weakness is one of the visible symptoms.
Indispensability is rewarded in practice
A leader whose function struggles in their absence is demonstrably important, and that is difficult to distinguish from a leader who failed to build capability.
The first interpretation is more flattering and equally consistent with the evidence, so it tends to be the one that prevails.
Organisations that want succession to work have to measure it, since the natural incentive runs the other way and does so quietly.
External appointments carry a different risk
Hiring from outside brings fresh perspective and no accumulated obligations, which is valuable where the organisation needs a change of direction.
It also means the new leader lacks the informal knowledge of how things actually work, and acquiring it takes time the role may not allow.
Where internal succession failed through insufficient development rather than deliberate choice, an external hire is treating a symptom at considerable expense.
Absence is the honest test
The condition of a function during a leader's extended absence shows what was genuinely transferred, in a way no assessment process can.
Leaders who never take that absence have no evidence about their own succession position, and they usually discover the answer at an inconvenient moment.
Arranging it deliberately, well before any transition is contemplated, converts an untested assumption into information that can still be acted upon.
What the absence reveals is usually specific: one or two decisions nobody else can make, which is a far more tractable problem than a general lack of readiness.