A recurring and entirely avoidable pattern: someone leaves for a role at another company that is materially similar to a role you had open, that you would have given them, and that they never applied for.
The reasons are mundane and they are almost all within a manager's control.
For a practical reference on task switching cost, Monitask provides read more.
Why it happens
They did not know the role existed. Internal openings are posted somewhere nobody reads, or filled before posting.
Applying internally is politically costly. Expressing interest in another team means telling your manager you want to leave. In many organisations that is a conversation with consequences, so people apply externally instead — where the process is confidential.
Their manager blocked it, or would have. Explicitly or by reputation. One manager who once blocked a move teaches an entire department not to try.
The internal process is worse than the external one. Slower, less responsive, less clear. A candidate who gets an external offer in three weeks and internal silence in six will take the offer.
They were told to wait. "Not yet, maybe next cycle" from someone with no authority to guarantee it.
Nobody asked what they wanted. The most common and simplest cause. The information was never gathered, so it could not be acted on.
The cost
Recruitment and ramp for the replacement, at a substantial multiple of salary once vacancy and productivity loss are counted.
The knowledge goes. Everything they knew about how things actually work here, which is the part not written down. See internal search and the knowledge that leaves with people.
You hire externally for the role they wanted, at market rate, with a ramp period, and with a higher failure rate than an internal move would have had.
Everyone watched. The people who remain now know that the way to change roles here is to leave.
What blocks it structurally
Managers are measured on team stability. A manager who loses someone to another team has a gap; one who keeps them does not. The incentive is unambiguous and it is rarely counteracted.
No visibility. Nobody knows what openings exist or what they require.
No sanctioned route. Expressing interest has no process, so it has to be done informally, which means politically.
Tenure rules that are too rigid. "Eighteen months in role before you can move" makes sense as a default and is applied as law.
Levels do not translate. Moving function means starting lower, and nobody explains whether that is temporary.
What actually works
Make managers accountable for internal moves out, positively. The single highest-leverage change and the hardest politically. If a manager is credited for developing people who go on to other teams — and the credit is real, appearing in their own review — the block dissolves. If it is only a stated value, it does not.
Publish openings internally first, with a real window before external posting.
Let people express interest without telling their manager. A confidential route to a talent or HR function. This is what the external market offers and internal processes usually do not, and it is the single biggest structural asymmetry.
Make the internal process faster than the external one. It should be. It usually is not, and there is no good reason.
Ask people what they want, on a schedule. Twice a year, as a real conversation, recorded somewhere. Most managers believe they know and are frequently wrong.
Offer trial arrangements. A rotation, a secondment, a project on another team. Lower stakes for everyone, and it surfaces mismatches before they become a bad move.
Be explicit about level translation. If moving function means holding level and rebuilding scope, say so, and say for how long.
For the individual
Say what you want, to someone. If your manager is not a safe person for that conversation, that is information — and it is usually the actual reason people leave.
Ask about internal openings directly, rather than waiting for a posting.
Ask what would need to be true. "What would I need to have done to be a candidate for that?" gets a concrete answer or reveals that there is not one.
Treat a blocked move as data. A manager who prevents you developing is not going to stop, and the calculation about staying should include that.
See seniority: what actually changes for what usually needs to be demonstrated, and titles and levels for what a move actually costs and gains.
The measurement
What proportion of open roles were filled internally, over the last year?
Most organisations do not know. The figure is usually lower than leadership assumes, and when it is broken down by department it identifies the managers who are blocking moves — which is uncomfortable, actionable, and the only way the problem gets addressed.
For broader public guidance and background, consult the OECD.