The only things you HAVE to know are how to make enough of a living to stay alive and how to get your taxes done. All the fun parts of life are optional.

"Forgot Algebra", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License

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The only things you HAVE to know are how to make enough of a living to stay alive and how to get your taxes done. All the fun parts of life are optional.