If only they'd worn a helmet...

I mean the hierarchy of control. IE the steps you take to reduce risk:
http://www.hse.gov.uk/risk/faq.htm#q1

1. Elimination - Redesign the job or substitute a substance so that the hazard is removed or eliminated.
   

2. Substitution - Replace the material or process with a less hazardous one.

3. Engineering controls - for example use work equipment or other measures to prevent falls where you cannot avoid working at height, install or use additional machinery to control risks from dust or fume or separate the hazard from operators by methods such as enclosing or guarding dangerous items of machinery/equipment. Give priority to measures which protect collectively over individual measures.

4. Administrative Controls - These are all about identifying and implementing the procedures you need to work safely. For example: reducing the time workers are exposed to hazards (eg by job rotation); prohibiting use of mobile phones in hazardous areas; increasing safety signage, and performing risk assessments.

5. Personal protective clothes and equipment - Only after all the previous measures have been tried and found ineffective in controlling risks to a reasonably practicable level, must personal protective equipment (PPE) be used. For example, where you cannot eliminate the risk of a fall, use work equipment or other measures to minimise the distance and consequences of a fall (should one occur). If chosen, PPE should be selected and fitted by the person who uses it. Workers must be trained in the function and limitation of each item of PPE.

PPE is used when after all the other means have been considered the risk is deemed still high (on a building site for example). However there are things you can do to minimise risk while climbing stairs, driving, cycling, crossing the road etc without needing to resort to ppe.

Which is why talking about helmets/PPE for the everyday activities I listed above detracts from really thinking about reducing risk, is a red herring.

Which is the point of this thread