# Keep shared failure causes in a fallback review

Illustrative planning brief; no automatic product import.

Synthetic planning case: Two alternate delivery routes use the same required input. In an invented model that input is missing with probability 0.1; both routes otherwise succeed. A proposal treats the routes as independent backups.

## Decision

Both routes fail together with probability 0.1 under the declared common-input model. Squaring 0.1 to obtain 0.01 would assume away the shared dependency.

## Owned work

- Map common prerequisites
  - Owner role: Route planner
  - Acceptance evidence: Both routes depend on the same named input.
- Inspect the joint failure conditions
  - Owner role: Reviewer
  - Acceptance evidence: The two supplied rows describe all events in the toy model.
- Choose a meaningful fallback
  - Owner role: Delivery lead
  - Acceptance evidence: Any alternative intended to bypass the input has its own verified requirements rather than a second route name.

## Workflow

1. Map common prerequisites. Check: Both routes depend on the same named input.
2. Inspect the joint failure conditions. Check: The two supplied rows describe all events in the toy model.
3. Choose a meaningful fallback. Check: Any alternative intended to bypass the input has its own verified requirements rather than a second route name.

## Judgment

Other failures are excluded by the toy definition. This does not estimate operational reliability or establish a real backup route.


## Filled manual planning note

Both routes fail together with probability 0.1 under the declared common-input model. Squaring 0.1 to obtain 0.01 would assume away the shared dependency. The only joint failure event is the shared missing input, with supplied probability 0.1. The false independent calculation 0.1×0.1=0.01 describes a different model. Naming two routes does not create independent redundancy. Other failures are excluded by the toy definition. This does not estimate operational reliability or establish a real backup route.


## Working artifact

- Shared input / Required by both routes / Inspect upstream availability
- Route A / Succeeds only if input exists / Not an independent bypass
- Route B / Same input condition / Retain joint failure condition


## Workflow questions

### Would a different executor remove this failure?

Not if that executor still needs the same absent input.

### Does 0.1 describe our real service?

No. It is a supplied illustrative probability with deliberately simplified conditions.

## Product connection

Use the owned checks and downloaded brief to discuss this planning decision alongside your TeamBoostAI tasks. Confirm available fields, roles and account features separately. The example is manual; it does not calculate live analytics, create work or run an experiment in the product.

Confirm account availability before adopting this manual outline.

## Original worked case

Synthetic records, manual planning only. No account import or live analytics.

### Inspect the invented case records

Toy condition | Probability | Route A | Route B
--- | --- | --- | ---
Shared input missing | 0.1 | Fails | Fails
Shared input available | 0.9 | Succeeds | Succeeds

### Reasoning

The only joint failure event is the shared missing input, with supplied probability 0.1. The false independent calculation 0.1×0.1=0.01 describes a different model. Naming two routes does not create independent redundancy.

### Bounded result

Both routes fail together with probability 0.1 under the declared common-input model. Squaring 0.1 to obtain 0.01 would assume away the shared dependency.

### Distinct decision

The worked case tests common-cause failure in an either-route plan, distinct from serial gates requiring both successes.

### Limits

Other failures are excluded by the toy definition. This does not estimate operational reliability or establish a real backup route.

### Definitions and method context

- Original worked-case definitions — Definitions, policy choices, records and calculations are authored for this worksheet. No external standard, statistical validation or live product measurement is claimed.