The "ABC Principle". Always Analyse (A) the problem first, only then start Building (B). Finally, don't move onto the next thing until you have Checked (C) that

The "ABC Principle". Always Analyse (A) the problem first, only then start Building (B). Finally, don't move onto the next thing until you have Checked (C) that whatever you've built matches up with your analysis. Applies to more than engineering as well.