Source and sink balance
Snapshot
~85 sec
Source and sink balance is not about matching totals once. It is about matching the rate an invented resource enters against the rate a legitimate decision can remove it, across a full session rather than a single moment.
You will learn
- Distinguish a source or sink total from a source or sink rate.
- Identify the two visible symptoms of an unbalanced flow: flooding and scarcity.
- Read a rate diagram to find which side of a loop needs a new rule.
Target outcome
You can look at a source and sink pair and state whether the flow is flooding, scarce, or balanced, and name the rate that needs to change.
Visual walkthrough
Visual walkthrough
~7 min
Four terms for reading resource flow
Source rate
How much of a resource a rule adds per unit of session time.
Sink rate
How much a rule removes per unit of session time when the intended decision is taken.
Net flow
Source rate minus sink rate over the same time window.
Balance point
The net flow value the system goal treats as the intended normal.
Two sources feeding one sink
A sink rate is never read against one source alone. Read this diagram top to bottom: both sources combine before the sink rate is ever compared.
Sources
Daily login source
Adds a fixed amount of the practice resource once per session start.
Practice match source
Adds a variable amount of the resource based on session length.
Shared pool
Practice resource pool
The running balance both sources add to and the sink removes from.
Sink
Upgrade choice sink
Removes the resource when the player takes the goal's intended decision.
- Daily login sourcePractice resource pooladds
- Practice match sourcePractice resource pooladds
- Practice resource poolUpgrade choice sinkspends
A sink rate is never read against one source alone. Read this diagram top to bottom: both sources combine before the sink rate is ever compared. Reading order
- Daily login source
Adds a fixed amount of the practice resource once per session start.
- Practice match source
Adds a variable amount of the resource based on session length.
- Practice resource pool
The running balance both sources add to and the sink removes from.
- Upgrade choice sink
Removes the resource when the player takes the goal's intended decision.
Connection explanations
- Daily login source → Practice resource pool (adds)
This source runs even on short sessions, so it sets a floor on the combined source rate.
- Practice match source → Practice resource pool (adds)
This source scales with play time, so the combined rate is not constant across players.
- Practice resource pool → Upgrade choice sink (spends)
The sink rate must be compared against the combined rate of both sources, never against either source alone.
Read the two visible symptoms
Approach Cause Visible signal Correct fix FloodingCombined source rate exceeds sink rate. A source rule adds faster than any legitimate sink removes. The pool balance keeps climbing and the sink decision starts to feel free. Add a legitimate sink or reduce a source rate; do not just raise the displayed price. ScarcitySink rate exceeds combined source rate. A sink removes faster than any source can supply. The pool balance keeps falling toward zero and the intended decision becomes rare or forced. Raise a source rate or remove a redundant sink; do not just lower the displayed price. Diagnose a growing pool
A pool has been growing for three weeks straight even though nothing was intentionally changed on the sink side. What is the first thing to check?
Expected reasoning
Check whether a new source rule, such as an event, a daily bonus, or an added session type, raised the combined source rate. A steadily growing pool is the flooding symptom, and the cause is almost always a source-side rate increase rather than a sink failing.