For guys learning FA - ETF’s are a good insight into investor thinking - they represent a simple means for an investor to gain exposure to a particular sector in stocks.
Sectors in turn provide an insight to market sentiment, if an investor is risk adverse they will seek to gain exposure ‘safe’ sectors such as utilities and so on - as John Murphy explains - ‘defensive’ sectors.
Then drilling down - if an investor is risk adverse they will not put their money into small caps, but on the other hand small caps offer a much better risk/reward in good times.
So check the russell 2000 to get a sense of thinking on risk.