What is the most important thing you weren't taught in school?

What topics are missing from the CS/IS education?

Posted so far

• How to sell an idea

Principles:

• Often, good enough is better than perfect.
• Making mistakes is actually a Good Thing™ -- as long as they're new mistakes.
• If a user can break your code they will.
• In the Real World™ they're all open-book exams
• Self confidence is way more important in getting ahead than intelligence.
• Always prefer simplicity over complexity. The best code is the code that you don't write.
• You never know when you'll meet someone again ... or where. It's always worthwhile to treat people with respect and kindness.
• Be aware of what you don't know and don't be afraid to ask questions when you need to

Missing knowledge:

• How to communicate effectively.
• Lack of source control
• Lack of Softskills experience
• How to productize code
• How to write secure code
• How to formulate problems
• How to self-measurement. To evaluate ones true competences and market worth.
• How to debug code
• How important is backup
• How to read code on a large scale (being able to adapt and build upon existing projects)
• Good Regular expressions comprehension
• How to teach others effectively
• TDD/Unit testing
• Critical thinking
• How to integrate different skills and languages in a single project