You're talking about market timing which is incredibly hard (some say impossible) to do over a long period of time. Sure, you might miss the down here (if there is one), but then you also might miss the move back up. There is a saying that time in market is much better than timing the market. If you consistently put money in, you'll naturally also buy the downs. At that point, you just need to periodically rebalance, and with age start to shift to less risky investments.