If you buy in the dip, that means you have extra money that's not invested.

If you have extra money not invested cause you're waiting for a dip, then you're not getting investment returns from the very long period of time we're not in a dip.

Even if you could predict the future, and determine when the bottom of a dip is so you could put all your money in, you're still going to come out worse than if you just invested in the first place.