Share your insights or perspective on the financial matter presented in the input.

Why invest for the long-term rather than buy and sell for quick, big gains?
The problem is that short-term trends are really unpredictable.  There is nobody who can accurately predict where a fund (or even moreso, a single stock or bond) is going to move in a few hours, or days or even months. The long-term trends of the entire market, however, are (more or less) predictable.  There is a definite upward bias when you look at time-scales of 5, 10, 20 years and more.  Individual stocks and bonds may crash, and different sectors perform differently from year to year, but the market as a whole has historically always risen over long time scales. Of course, past performance never guarantees future performance.  It is possible that everything could crash and never come back, but history shows that this would be incredibly unlikely.  Which is the entire basis for strategies based on buying and holding (and periodically rebalancing) a portfolio containing funds that cover all market sectors. Now, regarding your 401(k), you know your time horizon.  The laws won't let you withdraw money without penalty until you reach retirement age - this might be 40 years, depending on your current age.  So we're definitely talking long term.  You shouldn't care about where the market goes over a few months if you won't be using the money until 20 years from now. The most important thing for a 401(k) is to choose funds from those available to you that will be as diverse as possible.  The actual allocation strategy is something you will need to work out with a financial advisor, since it will be different for every person.  Once you come up with an appropriate allocation strategy, you will want to buy according to those ratios with every paycheck and rebalance your funds to those ratios whenever they start to drift away.  And review the ratios with your advisor every few years, to keep them aligned with large-scale trends and changes in your life.