TB: Opportunity Cost

The value of the best alternative foregone when making a choice. Every decision is implicitly a rejection of other options; the true cost of any action includes what you give up by not taking the next-best alternative.

Most people evaluate decisions by comparing the costs and benefits of the chosen option in isolation. Opportunity cost forces comparison against the next-best alternative — which is often the more relevant benchmark. Time is the most important domain: every hour spent on X is an hour not spent on Y; the question is never "is X valuable?" but "is X more valuable than Y?" Ignoring opportunity cost produces systematic over-commitment to sub-optimal uses of time and capital. The economists' framing — there is no free lunch, only traded costs — is one of the most useful thinking tools across domains.

• Poor Charlie's Almanack (Munger): Munger's "opportunity cost hurdle rate" — evaluate each investment against the best available alternative, not against zero; this is why great investors pass on most deals
• Seeking Wisdom (Bevelin): opportunity cost as a first-principles economic tool; Bevelin pairs it with incentives — understanding what someone gives up to do X reveals their true priorities

• Sunk Cost Fallacy — sunk costs are past; opportunity cost is future-facing; confusing them is a common error
• Second-Order Thinking — opportunity cost is the first second-order consequence of any choice