One senior engineer or two juniors on the same budget
A Series B team with one open requisition and a delivery commitment eight months out. The decision turned on who would do the mentoring, and that question had no good answer.
The decision timeline
Three moments, kept separate. What became known later sits in its own column so it cannot be read back into the reasoning.
Known at the time
- Fixed budget, seven weeks of requisition life
- Review, not implementation, was the throughput bottleneck
- A committed June migration with named customers attached
- No internal data on ramp time
Decided, and why
- One senior hire, because no one on the team could mentor two juniors through a migration
- Job description scoped to the migration, to shorten the search in a seven-week window
Known later
- The migration shipped three weeks late — the hire reduced the risk but did not eliminate it
- The mentoring gap surfaced as a retention issue for two existing engineers
- The review bottleneck halved, suggesting the capability read was right
Trust and provenance
What we checked, and what we did not.
The decision context
| Problem | One approved requisition at a senior band. The same budget would fund two mid-level hires. A platform migration was committed for the following June. |
|---|---|
| Deadline | Requisition expired at the end of the quarter; unused budget returned to the pool. |
| Stakes | Moderate |
| Decision-maker | Head of Engineering, with Finance approving the band split. |
Constraints
| Budget | Fixed envelope. Two mid-level offers fit; two senior offers did not. |
|---|---|
| Time | Seven weeks of requisition life. Senior pipelines in this market ran ten to fourteen weeks. |
| Information | No reliable internal data on ramp time — the team had only hired four people in two years. |
| Authority | Could split the band without further approval; could not carry budget into the next quarter. |
| External | Two competitors in the same city had just announced hiring freezes, loosening the market. |
Alternatives
Options considered, and the stated reason each rejected option was rejected.
Evidence available at the time
Including the assumptions that were never tested and the things nobody knew.
Available data
- Three months of sprint throughput showing review as the bottleneck, not implementation
- Two external recruiter market reports on senior availability
- A migration scoping document with a named critical path
Source types
Issue tracker export · Recruiter market reports · Internal scoping document
Assumptions
- That a senior hire could be productive on the migration within eight weeks
- That the loosened market would hold for the length of the search
Unknowns
- Whether the review bottleneck was a capability problem or a process problem
- Whether two mid-level hires would have been retained longer than one senior
Reasoning
Decision criteria
- Reduces risk on the committed June migration
- Does not increase the mentoring load on an already-stretched team
- Fillable within the requisition window
Trade-offs accepted
- Long-term team capacity against short-term delivery risk
- A single point of failure against two slower ramps
- Hiring for the migration against hiring for the three years after it
Risk tolerance
Low. A missed June commitment had named customer consequences; a thinner team in 2027 did not.
Action taken
| Chosen | One senior hire, scoped explicitly to the migration critical path. |
|---|---|
| Implemented | Rewrote the job description around the migration rather than the general role. Offer accepted in week six of seven. Started in week eleven. |
Outcome
Measured over: Twelve months, to August 2026
Results
- Migration shipped three weeks late against a June commitment — within the contractual grace period.
- Review turnaround time halved within two months of the hire starting.
- The hire was still with the team at twelve months.
Unintended consequences
- Two mid-level engineers who had expected mentorship from a new senior got a colleague fully absorbed by the migration instead. One raised it in a review cycle.
- The migration-shaped job description made the role harder to redefine afterwards.
Reflection
| What changed | Requisitions now carry an explicit note on who absorbs the mentoring load, written before the role is opened. |
|---|---|
| What was learned | I framed this as a seniority decision when it was really a question about mentoring capacity. Once I saw that, the answer was forced — and that is a sign the real constraint had been invisible for months. |
| Would do differently | I would have tested whether the review bottleneck was process rather than capability before spending a requisition on it. It is entirely possible a change to review assignment would have bought the same throughput for free. |
Transferability
The conditions under which this lesson applies — and the conditions under which it does not.
Applies when
- There is a dated, externally-visible delivery commitment
- The existing team has no slack for mentoring
- The budget envelope genuinely forces the choice
Does not apply when
- The team has mentoring capacity — the maths then favours two hires
- There is no hard delivery date, which removes most of the pressure toward seniority
- Your retention risk on a single senior hire is high
Rights and licensing
Published terms for this case.
| Consent | Creator confirms permission to publish anonymously with employer redacted. |
|---|---|
| Licence | Non-exclusive, perpetual licence to publish and monetise. |
| Anonymisation | Creator name, employer and all customer names withheld. |
| Compensation | Eligible for the creator revenue pool under the published allocation rule. |
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