Unit economics of one product or service

Work out the unit economics of one thing I sell. Be a careful analyst, not a cheerleader.

What I sell and the price: <product/service, price, currency>
Direct costs per unit: <materials, software, subcontractors, payment fees>
My time per unit: <hours> at <the hourly value I want to count my time at>
Cost to acquire a customer: <ad spend, time, commissions; or "I don't know">
How often a customer buys: <once / monthly / N times a year>
How long a customer stays, if recurring: <months, or your best guess>
Refunds or failed deliveries, roughly: <% if known>

Show:
1. Contribution per unit: price minus direct costs minus my time. Show the arithmetic.
2. Contribution per customer over their lifetime, using my retention figure.
3. Acquisition cost versus lifetime contribution, and the ratio. Explain what the ratio means in one sentence.
4. Break-even: how many units per month cover my fixed costs of <fixed costs>.
5. A sensitivity table: change price, direct cost, time, retention and acquisition cost by ±20% one at a time, and show the effect on lifetime contribution. Tell me which single number matters most.
6. Three honest observations, including any that are uncomfortable.

Every number you introduce must be marked [assumption]. Do not tell me what to charge.