A founder asked us for one backend developer for a couple of months. We said yes, staffed it that way, and then watched what the work actually turned into: the first weeks were almost entirely infrastructure and deployment setup, the middle stretch was getting a mobile release through store review, and only the tail end was the backend work he had originally described.
One person covered all of it. He could, technically. But he spent most of those weeks outside his strongest lane, so everything took longer and he carried a quiet kind of stress the budget had not accounted for. The founder paid for a backend engineer and got a slower version of three different specialists.
That one is on us for taking the request literally. A project does not need a developer, it needs whatever the current phase needs, and that changes every few weeks. So now we scope the way we would staff our own work: which roles does this stage actually need, and for how long. Infra early, QA before a release, backend when the feature work lands. Roles rotate in and out, the project keeps its context, and people are not pretending to be specialists in something they touch twice a year.
The side effect we did not expect is that it got easier to explain. "Two weeks of DevOps, then a mobile release cycle" is something a founder can sanity-check. "One senior developer" tells him very little about what he is getting.
If you have brought in outside help before, it is worth looking back at whether you scoped it by person or by the work. The second one probably aged better.