Canonical definition
Would you sell something only for much more than you’d be willing to pay for it? That’s Endowment Effect – the tendency to overvalue things just because you own them.

Free cognitive-bias Agent Skill
Use Endowment Effect as a focused cognitive-bias lens. Explain the pattern, check whether it plausibly fits the situation, surface an alternative non-bias explanation, and return a practical counter-check without diagnosing people or claiming causation.
What the agent should do
Would you sell something only for much more than you’d be willing to pay for it? That’s Endowment Effect – the tendency to overvalue things just because you own them.
Install
Hermes Agent
mkdir -p ~/.hermes/skills/bias-prospect-theory-endowment-effect && curl -fsSL https://cognitive-biases.github.io/agent-skills/bias-prospect-theory-endowment-effect/SKILL.md -o ~/.hermes/skills/bias-prospect-theory-endowment-effect/SKILL.mdOpenClaw
mkdir -p ~/.openclaw/workspace/skills/bias-prospect-theory-endowment-effect && curl -fsSL https://cognitive-biases.github.io/agent-skills/bias-prospect-theory-endowment-effect/SKILL.md -o ~/.openclaw/workspace/skills/bias-prospect-theory-endowment-effect/SKILL.mdOther Agent Skills-compatible tools
Download SKILL.md and put it in the skill directory or import surface supported by your agent.
Boundary
The skill must preserve uncertainty, surface a non-bias explanation and avoid turning a cognitive-bias label into a claim about a person's motives, intelligence or mental health.