(Sorry, genuine questions) risk of what and compared to what?
One of many, the housewives who saved money from day to day house expenses, had to come out clean to family that they are holding 1000s of currency in old now defunct notes.
Yes, there's inflation negative yield. But especially in the low interest and inflation rate environment that has been the case until possibly recently, the difference between "cash" (i.e. default investment at a brokerage) and other very low-risk investments (e.g. high quality corporate bonds) has been pretty minimal.
Bet on humanity :)
If you've not watched The Big Short (2015)[0], it's a really excellent film.
Nothing you do in life is risk free, even keeping cash under your mattress: the fact that there is risk involved does not change that this is how you make money. When you know that you’re guaranteed a loss of ~2%, at best, on cash, and that your expected real return on stocks is positive, well… That’s the point.
At least in the UK, buying into index funds was substantially more expensive back then. I held shares in a retail bank for a time not long after that, for which I had an actual paper certificate! No wonder trading was expensive....
Except when you don't.
Between 1995 and 2000 I lived in a student house in the UK and one of my housemates (who was also a student, and from my recollection almost as broke as I was back then) was really into investing into the stock market during the dot-com boom.
He bought both Lastminute.com (IPO March 2000 @ 380p/share[1], sold to Travelocity in 2005 @ 165p/share[2]) and Railtrack (IPO 1996[3], went bankrupt 2001[4])
[1] https://money.cnn.com/2000/03/14/europe/lastminute/ [2] https://www.theguardian.com/technology/2005/may/13/business.... [3] https://www.railwaysarchive.co.uk/docsummary.php?docID=740 [4] https://www.independent.co.uk/news/uk/home-news/railtrack-go...