Promises are only as strong as those who make them; thus those made by Theresa May were doomed to dissolve from the time she delivered them.
The latest "protocol" offered by Boris Johnson to replace the backstop in Mrs May's original Withdrawal Agreement also looked troublingly liquid.
Taoiseach Leo Varadkar was suitably diplomatic in his response, merely saying it "falls short".
Mr Johnson has argued the backstop is "a bridge to nowhere". Alas, the slight proposals set down yesterday look like a flimsy pontoon that could be washed away in the first tides of trouble.
They require stronger foundations to either protect the legacy of the Good Friday Agreement, or seal the single market. They are more an outline than a detailed plan.
In a letter to Jean-Claude Juncker, Mr Johnson warned inability to reach a deal would be a "failure of statecraft for which we would all be responsible".
In apportioning blame there is always more than enough of it to go around.
A breach in the commitment to avoid Border checks is incompatible with a meeting of minds. The package requires Brussels to grant the UK sweeping exemptions from EU customs rules.
The "shift" in emphasis for Mr Johnson seems to have gone from a "backstop" to a "frontstop". We must take care it all does not end in a full stop.
A delay is now required to see if there can be any more movement. Mr Johnson may soon have his election. A degree of stability in government must be re-established. It is improbable Mr Johnson can come up with anything that would get past Parliament. What is currently on the table asks too much and delivers too little.
Anything short of an invisible Border could undermine the Good Friday Agreement and peace on this island.
So acceptance for both a regulatory border between Britain and the North in the Irish Sea for four years, plus North/south customs checks to replace guarantees already signed off on, seems a very hard sell as things stand.
Surrendering something tried, trusted and secure, for something that could result in a permanent Border does not seem a reasonable demand.
Commitments cannot be exchanged for vague possibilities. The Brexiteers fear the UK could be trapped indefinitely in limbo, but they have no problem inviting the same plight on the North. Rejection of the latest Brexit plan may lead to the no deal Mr Johnson warned of.
But acceptance could have the same negative outcomes. The British prime minister claims his plan is reasonable. But the risks appear weighed too heavily on one side.
Stepping from the concrete onto such shifting sands demanded a far more persuasive case than the one delivered yesterday by Mr Johnson.
A deal when it is struck will have to be balanced, supporting the interests of both sides.
There will have to be more talking.
But the art of conversation is the art of hearing as well as of being heard.