The distinction
Upskilling raises a person's level in a capability they already hold — moving from Intermediate to Advanced in something they use weekly. Reskilling moves a person into a different capability, usually because the work they were doing is changing or disappearing.
The reason to keep the words separate is not tidiness. They differ in cost, in timescale, in failure rate, and in how you would know whether either had worked, so a plan that does not say which one it is cannot be resourced or judged properly.
Why upskilling is the easier investment
Upskilling starts from a known baseline. The person has context, the vocabulary and a reason to care, so the distance to cover is short and the progress is legible — a level moves, and the movement is verifiable against the same standard that set the baseline.
It also fails safely. Someone who attempts Advanced and stays at Intermediate is exactly where they started, which is not a loss. That asymmetry is why most development budget should go here, and why most of it does not.
What reskilling actually requires
Reskilling is a bet with a longer payback and a genuine failure mode: someone spends months on a capability they never reach a useful level in, while getting worse at the thing they were already good at. That risk is manageable but only if it is acknowledged in the plan rather than discovered later.
It needs three things upskilling does not. A longer horizon before anyone judges it. Real time protected from the person's existing job, rather than the expectation that it happens in the gaps. And an honest checkpoint partway through, where continuing is a decision rather than a default.