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It is a capital mistake to theorize before one has data.
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“It is a capital mistake to theorize before one has data.”

Arthur Conan Doyle

Source
A Scandal in Bohemia
Date
1891
Meaning

Meaning of “It is a capital mistake to theorize before…”

Holmes argues that explanations should follow evidence because an early theory can tempt a person to force later facts into a preferred story.

Source context

Where does it come from?

“A Scandal in Bohemia,” The Adventures of Sherlock Holmes (1891), Project Gutenberg #1661. Holmes immediately warns that premature theorizing leads people to twist facts to suit theories; it is fictional detective dialogue.

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DeepLifeLife LessonsMindShortThinking Quotes About Reasoning, Reflection & JudgmentThought-Provoking Quotes That Invite ReflectionTruthUnderstandingWisdom Quotes About Judgment & Living WellKnowledgeMistakesPerspectiveReason
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“A long habit of not thinking a thing wrong, gives it a superficial appearance of being right.”

Thomas Paine · Common Sense · 1776
Meaning & context

Custom can disguise error by making the familiar feel legitimate; critical judgment requires re-examining practices that have escaped scrutiny through repetition.

Source details

Common Sense (1776), Introduction. The represented opening sentence is verified in Project Gutenberg #147 and the validated scan-backed Wikisource transcription; Paine argues that familiarity can make a wrong practice appear right before public argument unsettles the custom.

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He who knows only his own side of the case, knows little of that.
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“He who knows only his own side of the case, knows little of that.”

John Stuart Mill · On Liberty · 1859
Meaning & context

Understanding a position requires serious contact with competing arguments; familiarity with only one side can produce confidence without real comprehension.

Source details

On Liberty, Chapter 2; Mill argues for open discussion because opposing views expose weaknesses and sharpen understanding.

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A hasty judgement is a first step to a recantation.
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“A hasty judgement is a first step to a recantation.”

Publilius Syrus · The Moral Sayings of Publius Syrus · 1856 translation
Meaning & context

Rushing to a conclusion increases the chance that later evidence will force an embarrassing or costly reversal.

Source details

The Moral Sayings of Publius Syrus, maxim 8, in Darius Lyman’s 1856 English rendering; maxim order can vary across editions.

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Read not to contradict and confute; nor to believe and take for granted; nor to find talk and discourse; but to weigh and consider.
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“Read not to contradict and confute; nor to believe and take for granted; nor to find talk and discourse; but to weigh and consider.”

Francis Bacon · Of Studies · 1625
Meaning & context

Bacon describes reading as active judgment rather than passive agreement or reflexive opposition, making careful consideration the central habit of serious study.

Source details

Of Studies, in Bacon’s instructions for how different kinds of books should be read.

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All men by nature desire to know.
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“All men by nature desire to know.”

Aristotle · Metaphysics · c. 350 BCE
Meaning & context

Aristotle treats the desire for knowledge as a basic human tendency, giving curiosity a foundational place in the movement from perception toward understanding.

Source details

Aristotle, Metaphysics, Book I, Chapter I, W. D. Ross translation (1908), validated Wikisource scan leaf 21. 'All men by nature desire to know' opens the work before the discussion of sensation, memory, experience, art and knowledge. This remains ancient philosophy mediated by translation, not a modern empirical finding about cognition.

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I am not young enough to know everything.
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“I am not young enough to know everything.”

J. M. Barrie · The Admirable Crichton · 1902
Meaning & context

Barrie reverses the cliché that age brings complete wisdom, making youthful certainty—not age—the comic claim to omniscience.

Source details

The Admirable Crichton, Act I, Project Gutenberg #3490. Ernest Woolley repeatedly delivers “I am not young enough to know everything” as a self-consciously clever epigram while Agatha, Treherne and the others struggle to understand it; Crichton later says he has no idea what Ernest meant. It remains fictional comic dialogue rather than J. M. Barrie autobiography or a factual claim about age and knowledge.