1. Inability to reason about codeReasoning about code means being able to follow the execution path ("running the program in your head") while knowing what the goal of the code is.SymptomsThe presence of "voodoo code", or code that has no effect on the goal of the program but is diligently maintained anyway (such as initializing variables that are never used, calling functions that are irrelevant to the goal, producing output that is not used, etc.)Executing idempotent functions multiple times (eg: calling the save() function multiple times "just to be sure")Fixing bugs by writing code that ov...