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The logic of the world is prior to all truth and falsehood.
— Ludwig Wittgenstein^[1]

A curated list of falsehoods programmers believe in. A falsehood is an idea that you initially believed was true, but in reality, it is proven to be false.

E.g. of an idea: valid email address exactly has one @ character. So, you will use this rule to implement your email-field validation logic. Right? Wrong! The reality is: emails can have multiple @ chars. Therefore your implementation should allow this. The initial idea is a falsehood you believed in.

The falsehood articles listed below will have a comprehensive list of those false-beliefs that you should be aware of, to help you become a better programmer.

Contents

• Meta
• Arts
• Business
• Cryptocurrency
• Dates and Time
• Education
• Emails
• Geography
• Human Identity
• Internationalization
• Management
• Multimedia
• Networks
• Phone Numbers
• Postal Addresses
• Science
• Society
• Software Engineering
• Transportation
• Typography
• Video Games
• Web

Meta

• Falsehoods Programmers Believe - A brief list of common falsehoods. A great overview and quick introduction into the world of falsehoods.
• Falsehoods about Programming - A humbling and fun list on programming and programmers themselves.
• Falsehoods about Falsehoods Lists - Meta commentary on how these falsehoods shouldn't be handled.

Arts

• Falsehoods about Music - False assumption that might be made in codifying music.
• Falsehoods about Art - Common misconceptions about art.

Business

• Falsehoods about Online Shopping - Covers prices, currencies and inventory.
• Falsehoods about Prices - Covers currencies, amounts and localization.
• Falsehoods about IBANs - International Bank Account Numbers are not international.
• Falsehoods about Economics - Economics are not simple or rational.
• Decimal Point Error in Etsy's Accounting System - The importance of types in accounting software: missing the decimal point ends up with 100x over-charges.
• Twenty five thousand dollars of funny money - Same error as above at Google Ads, or the danger of separating your pennies from your dollars, where $250 internal coupons turned into $25,000. My advice: get rid of integers and floats for monetary values. Use decimals. Or fallback to strings and parse them, don't validate.
• “The system can’t handle a billion dollars” - Insane compensation at Meta in the middle of the AI-boom breaks ERPs.
• Characters < and > in company names lead to XSS attacks - Because UK allows companies to be registered with special characters, a hacker leveraged them to register \"><SCRIPT SRC=MJT.XSS.HT></SCRIPT> LTD, but also ; DROP TABLE "COMPANIES";-- LTD, BETTS & TWINE LTD and SAFDASD & SFSAF \' SFDAASF\" LTD.