A fantastic book I recently read, here are my notes on it:
What distinguishes Holmes from most mortals is that he knows where to look and what questions to ask.
Holmes first gathered all the evidence he could that was relevant to his problem. At times, he performed experiments to obtain fresh data. He then surveyed the total evidence in the light of his vast knowledge of crime, and/or sciences relevant to crime, to arrive at the most probable hypothesis. Deductions were made from the hypothesis; then the theory was further tested against new evidence, revised if need be, until finally the truth emerged with a probability close to certainty.
But only what is useful – it can be dangerous to know too much
All the knowledge which he possessed was such as would be useful to him.
With every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.
It is useful to know something about human nature and what motivates people
Work is the best antidote to sorrow,
Sorrow is often wisdom’s companion but it is better to learn from others sorrow to prevent our own
Note: Learn from the mistakes of others
Never jump to conclusions and try to collect facts as open-minded as possible
Dont make hasty judgments.
It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.
The fatal mistake which the ordinary policeman make is this, that he gets his theory first, and then makes the facts fit it,
Observation – Start with collecting facts and follow them where they lead
More is missed by not looking than not knowing.
We can’t observe or collect facts without some kind of view – what to look for, how to look and how to interpret what we see
Make sure “facts” are facts – Is it really so? Is this really true? Are there exeptions?
Don’t miss the forest for the trees – It is not the amount of information that counts but the relevant one.
More information isn’t necessarily better information but it may falsely increase our confidence – What is not worth knowing is not worth knowing
“A wise man sees as much as he ought, not as much as he can.”
We need to both observe the big picture – forest – and the details – trees.
Reasoning backwards – working back from observations/effects to causes
Note: Reverese Engineering
Before you try a complicated hypothesis, you should make quite sure that no simplification of it will explain the facts equally well.
But don’t try to over-simplify complex matters – especially when we deal with systems with complicated interactions
History often repeats itself There is nothing new under the sun. It has all been done before. So look for lessons in history
But sometimes we learn more by looking for differences – not similarities – in situations
But remember that we see what we are looking for – if we look for similarities, this is what we see, if we look for the differences, that is what we find.
Eliminate possibilities – What can we exclude? – Assuming the true solution or explanation is among the considered possibilities old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth.
These deductions, gentlemen, must however be confirmed by absolute and concrete evidence…Never neglect to ratify your deductions.
Facts don’t lie but we may have interpreted or stated them wrong and therefore drawn the wrong conclusion
Distance gives perspective – Sometimes we need to remove ourselves from the problem and get a fresh perspective
Put yourself in the other person’s shoes
It we could see the world the way others see it, we easier understand why they do what they do
A rule is only a rule if it’s always true!
Watch out for overconfidence
Do we really have an important case? Deal with things that really matter and that we can do something about
Don’t think about how to get things done, instead ask whether they’re worth doing in the first place