I think about this chart often during discussions with clients on having too much exposure to single stocks.
While Citigroup (red) is up 32% for the last two years, you would still only have $164 for your $100 investment when it went public almost 30 years ago. Your same $100 investment would be worth $1,721 if invested in the S&P 500 (blue) or a whopping $2,341 if invested in JPMorgan Chase (orange).
With large single stock holdings, we see risk. There is a 50% chance your investment could fall and never really recover, like a Citigroup, or a 50% chance you get fantastic returns, like a JPMorgan Chase.
This risk can be mitigated with well-diversified investments, like the S&P 500, which over multiple 20-year time spans going all the way back to 1926 has been positive 100% of the time.