Having faith in people is commendable but the past two years have taught us many are not responsible with money. What looks good on paper and what actually happens is another story and there sure as hell is never a sure bet in terms of investing at least not in my opinion and I also don't think a one size fits all approach works.
The stock market has returned about 10% annually since 1926...nearly 100 years.
Seems like a pretty sure thing to me but you're right... theoretically, nothing is forever I suppose.