Causes of Bugs

1. Misunderstanding.

   • Difficult to read code and grasp the concept.
   • Not reading documentation.
   • Reading documentation – documentation and code mismatch.

2. Lack of awareness.

   • Values are changed by "some other code".
   • Behaviour changes on upgrades.
   • Operating with invalid values.

3. Mental overload.

   • Difficulty in expressing concept as code.
   • Too many things to keep track of.

4. Changing expectations.

   • What was desired previously is now undesired.
   • Subset of code is changed to meet new expectation.