Followed by “you must have a boat to begin with.”
Or, rising tide raises the wealthy yachts so high into rarefied air that they are no longer in touch with the regular folks. You are no longer a person of value. (Still trying to make it pithy.)
Or, in terms of environmental impact, the rising tide just inundates lands, drowning people. Those with boats ride to safety.
Whatever, it is clear that phrase is no longer valid in light of the eye-popping gains the 1% and profit hoarding corporations have made at the expense of the rest of the folks.
This phrase first popped into national lexicon during the 60’s, the halcyon days of middle class prosperity.