8 mental models for everyday decisions
- Inversion — instead of asking how to succeed, ask what would guarantee failure, then avoid it.
- Second-order thinking — ask “and then what?” A cheaper supplier saves money now; what happens when deliveries start running late?
- Reversibility — easy-to-undo decisions can be made fast; hard-to-undo ones deserve a check first.
- Opportunity cost — every yes is a no to something else. What are you giving up?
- The load-bearing assumption — find the one fact the whole plan depends on, and check it.
- Small steps — commit in stages so each step earns the next, instead of going all in too soon.
- Base rates — before trusting your plan, ask how this usually goes for other people.
- Sunk cost — decide on what happens next, not on what you've already spent.
How to use mental models without overthinking
Don't try to apply all eight. Pick the two that fit: for big money decisions, inversion and opportunity cost; for anything hard to undo, reversibility and small steps.
Question → Test → Decide → Learn puts the most useful models into one short routine: inversion in Question, the load-bearing assumption in Test, small steps in Decide, and review in Learn.
Frequently asked questions
What are mental models in simple terms?
Shortcuts for seeing a problem from a useful angle — like asking “what would make this fail?” before asking how to succeed.
Which mental model is the most useful?
For everyday decisions, inversion (or a pre-mortem). Imagining failure first surfaces risks you'd otherwise miss.
How many mental models do I need?
A handful used often beats dozens you never apply. Start with inversion, reversibility and opportunity cost.