The theory that index/passive funds perform better than actively managed funds is backed by the fact that 90% of active funds underperformed their benchmarks over the last 10 years. So, it begs the question, “Why?”
Firstly, index funds do not have the added expenses of investment analysists and advisors, lowering overall cost and ultimately leaving more returns for investors to keep.
The chart above from S&P Dow Jones Indices shows the average actively managed fund costs 0.68% versus index funds of only 0.06%. So, right off the bat, every year the actively managed fund starts 0.62% in the hole.