A mother instructs her child not to run too fast, not to run outside the given track in the garden, not to run without sports shoes, etc. etc.
She'd seen the child injuring herself earlier in absence of observing the discipline of 'not-to' such as above.
Another mother sitting next to her appeared appreciative. She didn't hesitate to share her experience of how her non-observant son had damaged his hamstring muscles irreversibly. She was concerned that her son had been living with the pain since years.
The pathological and clinical tests, investigations, analysis and treatments are now companion for the lifetime, she said.
Question is, is the former approach, the 'nagging' one, correct?
Obviously, but not so obviously!
Former approach can be called as judgemental based on seed-stage deviations that probably were thought to lead to major deviations or crises if not kept under check. It's about commonsensical risk management.
Latter one, the one that involved accidents and treatments, is an analytical approach that reactively analyses major deviations already occurred.
Former one is based on real-time (genjitsu) observations of real-facts-and-conditions of things and people (gembutsu) at the real-place of happening (gemba).
Latter one usually needs extensive analysis. At times it leads to 'paralysis-by-analysis' that necessitates intervention of judgement in order to unlock the tie and move ahead.
Former approach is easy, fast and proactive although seems to appear like 'nagging'. Of course it is expected to incorporate factual learnings from past.
The latter is difficult, time-consuming and reactive one. It's usually a post-mortem that often necessitates involvement of specialist agencies. Most often it results into repentance of irreversible damage and costs.
Importance of structured analysis however can't be undermined particularly if it's for exploratory or descriptive research in order to study cause-effect relationship of an hypothesis on an observed phenomenon in real-time (genjitsu) or for future innovations.
Also read a few relevant blogposts hereunder:
Prevention: The Best Cure! ... Is it really so? 
Treat Root-causes, Not Symptoms ! 
When Safety Becomes Sorry 
Drove To Hell ... Almost !  
WOW Work-Culture: By Telling or Selling 
Take Habits For A Ride 
How Many Times Do You Wash Hands 
In a Problem?: No Problem ! Dwell A While !! 
Part-1
In-big-problem? Wear-hats-to-solve-it! Part-2 
How To Make A Difference 
Big-Be Or Bug-Be ! 
A Ride To Hell 
Make checklists your friends 
Nauseous Communication Gaps 
Do You Cleanup-After-Crisis 
Raam or Krishna-Shyam: Tell me Hey Raam! 
Will It Work Here?  
That's How Morons Work
You seem Reasonable if you appear Un-reasonable 
Smart-Moron Who Breaks Your Glass  
Wish To Be Planet-Friendly?: Save!  
Waste-to-eat-sea-to-drink
Don't Save Water on Holi-day 
Be Shame-less Or Water-less