Assumption
A claim you are treating as true for the design, often about traffic shape or user behavior. Wrong assumptions become risks.
Definition
An assumption is something you believe is true for the design.
If the assumption is wrong, the design can break.
Why it matters
Assumptions are where hidden risk lives.
Write them down so you can validate them later.
How to handle assumptions well
- Make them specific: “peak-to-average is 10×.”
- Say how you would validate: logs, metrics, experiments, business data.
- Say what breaks if it is wrong: “cache hit rate drops, DB load spikes.”
Real-world examples
- “Most requests are reads. Writes are rare.”
- “A small set of keys will be hot.”
- “We can tolerate eventual consistency for analytics.”
- “We can ship v1 without feature X.”