Buying the dip is even harder to do in these bubble markets where all assets are rising and dipping in sync. It is easier to do in markets when the different asset classes are uncorrelated or even better if you have asset classes that have negative correlation.
When something is at a dip another asset is at a peak and you can sell that asset high in order to buy something low, but again that is really hard to do in this market where asset classes are all rising simultaneously. You could hold cash so that you can have some "dry powder", but over the course of this last year there has been a heavy cost to being on the sidelines with cash.
RE: You can't afford to buy the dip unless you're selling.