The angled lines enable more detail to be added than lines at right angles to one another,
especially in an informal situation where causes are being added 'on the fly'.
Each line indicates either a named cause or a cause area which contributes to the cause line to which it is attached.
A cause area is not a cause, but may contain causes.
For example, a tire may be a cause area but may not be a cause of an accident.
A smooth or punctured tire can be a cause. Cause areas tend to be nouns, whilst causes tend to use verbs.