Here's why investing in the long run may be beneficial:

To sleep peacefully. Knowing that the main part of your assets will not be used soon, you only have to do with the daily volatility of the stock markets. You know full well that time becomes your ally and that in the long run, the risk of loss magically vanishes. No need to consult nervously every day your earnings. A thorough analysis of the results every three months or six months will do the trick.