Can you understand the business? Is it in your circle of competence? Avoid industries where you know little.
Does the business have a moat? Does it have a durable competitive advantage? Avoid perfectly competitive and high fixed cost industries.
Does it have managers that behave as owners and are wise capital allocators?
Do insiders own their own stock and are they buying back shares?
Does the company have a lot of debt? Any long list of numbers multiplied by zero is always zero.
Details
Risk: All investment evaluations should begin by measuring risk, especially reputational
Incorporate an appropriate margin of safety
Avoid dealing with people of questionable character
Insist upon proper compensation for risk assumed
Always beware of inflation and interest rate exposures
Avoid big mistakes; shun permanent capital loss
Independence: "Only in fairy tales are emperors told they are naked"
Objectivity and rationality require independence of thought
Remember that just because other people agree or disagree with you doesn't make you right or wrong-the only thing that matters is the correctness of your analysis and judgment
Mimicking the herd invites regression to the mean (merely average performance)
Preparation: "The only way to win is to work, work, work, work, and hope to have a few insights"
Develop into a lifelong self-learner through voracious readings cultivate curiosity and strive to become a little wiser every day
More important than the will to win is the will to prepare
Develop fluency in mental models from the major academic disciplines
If you want to get smart, the question you have to keep asking is “why, why, why!"
Intellectual Humility: Acknowledging what you don't know is the dawning of wisdom
Stay within a well-defined circle of competence
Identify and reconcile disconfirming evidence
Resist the craving for false precision, false certainties, etc.
Above all, never fool yourself, and remember that you are the easiest person to fool
Analytic Rigor: Use of the scientific method and effective checklists minimizes errors and omissions
Determine value apart from price; progress apart from activity; wealth apart from size
It is better to remember the obvious than to grasp the esoteric
Be a business analyst, not a market, macroeconomic, or security analyst
Consider totality of risk and effect; look always at potential second order and higher level impacts
Think forwards and backwards-Invert, always invert
Allocation: Proper allocation of capital is an investor's number one job
Remember that highest and best use is always measured by the next best use (opportunity cost)
Good ideas are rare-when the odds are greatly in your favor, bet (allocate) heavily
Don't "fall in love" with an investment-be situation-dependent and opportunity-driven
Patience: Resist the natural human bias to act
"Compound interest is the eighth wonder of the world" (Einstein); never interrupt it unnecessarily
Avoid unnecessary transactional taxes and frictional costs; never take action for its own sake
Be alert for the arrival of luck
Enjoy the process along with the proceeds, because the process is where you live
Decisiveness: When proper circumstances present themselves, act with decisiveness and conviction
Be fearful when others are greedy, and greedy when others are fearful
Opportunity doesn't come often, so seize it when it does
Opportunity meeting the prepared mind: that's the game
Change: Live with change and accept unremovable complexity
Recognize and adapt to the true nature of the world around you; don't expect it to adapt to you
Continually challenge and willingly amend your "best-loved ideas"
Recognize reality even when you don't like it - especially when you don't like it
Focus: Keep things simple and remember what you set out to do
Remember that reputation and integrity are your most valuable assets-and can be lost in a heartbeat
Guard against the effects of hubris and boredom
Don't overlook the obvious by drowning in minutiae
Be careful to exclude unneeded information or slop: "A small leak can sink a great ship"
Face your big troubles; don't sweep them under the rug
Other
The Two-Track Analysis
What are the factors that really govern the interests involved, rationally considered? (for example, macro and micro-level economic factors).
What are the subconscious influences, where the brain at a subconscious level is automatically forming conclusions? (influences from instincts, emotions, cravings, and so on).
Investing and Decision Making Checklist
Charlie's informal, but extensive, list of factors worthy of consideration.
Ultra-Simple, General Problem-Solving Notions:
Decide the big "no-brainer" questions first.
Apply numerical fluency.
Invert (think the problem through in reverse).
Apply elementary multidisciplinary wisdom, never relying entirely upon others.
Watch for combinations of factors-the Lollapalooza effect.
Psychology-Based Tendencies
His famous Twenty-Five Standard Causes of Human Misjudgment