Opportunity Cost
Every choice means giving up something else.
Explanation
Every choice you make automatically eliminates other options. When you choose to spend an hour watching TV, you're not just 'spending' that hour—you're giving up an hour you could have used for exercise, learning, or connecting with family. This hidden cost of giving up alternatives is often more important than the direct cost of what you choose.
Real-World Example
Meeting for 1 hour = not shipping code = delayed feature = lost revenue. Keeping $10k in savings account at 0.5% instead of index fund at 10% = losing $950/year. Saying yes to coffee with acquaintance = saying no to deep work = project delayed. Netflix spending $17B on content = not spending on technology = eventually losing to Disney+.
How to Apply
Before committing: List top 3 alternatives. Estimate value of each. True cost = value of best alternative. Only proceed if gain > opportunity cost. Use time blocking: schedule important work first, fit other things around it. Money decisions: calculate in life hours (is this $100 item worth 3 hours of your life?).