The first mistake internal successors make is being good at their old job
Promoting from within removes the learning curve and introduces a different failure: two jobs, one person, six months.
The argument for internal succession is well rehearsed: no learning curve, no cultural mismatch, no six-month orientation. The argument is correct, and it conceals the specific way internal successions fail.
An external chief executive cannot do their predecessor’s job, or their own previous one, because they do not know how. An internal successor can do their previous job extremely well, and will, because it is the part of the week that produces visible results while the new role produces mostly meetings.
The six-month overlap
The pattern is consistent. The new chief executive retains their old function informally — attending its reviews, resolving its escalations, being copied on its decisions — while a successor is "given time to settle". The successor does not settle, because the organisation can see who still makes the decisions.
The alternative was two people doing one job badly.
Rahul Menon, Chief Executive Officer, Arclight Systems
The fix is uncomfortable and cheap: hand the previous role away before the successor is ready, and accept a visible dip in that function’s performance. The dip is real. It is also shorter and less damaging than a year of ambiguous authority.
What boards should ask
Not "is the successor ready", which is unanswerable and invites delay, but "on what date does the new chief executive stop attending their old function’s operating review". A date is checkable. Readiness is not.