For MEB, always.
John Maynard Keynes was among the most important economists in history, if the author is more of a Schumpterian, who had an argument with Keynes useful in understanding things now.
Joseph Schumpeter was an academic, the creator of the vital notion of capitalism as a process of Creative Destruction, among other things, who also foresaw the modern tension between democracy and capitalism very well, and who criticized Keynes for having too short a term mentality.
The first Keynesian aphorism in question is "In the long run, we're all dead," which was in response to Classically trained economists like Schumpeter's criticism of Keynes that he ignored the long run too much in his analysis, which was in fact a valid criticism, if Keynes wasn't all wrong either; it depends on timing as to which is more accurrate between the Classical and Keynesian view, if also politics, since politicians have shorter time horizons as to elections.
Some of that differece over time perspective was because Keynes was a practitioner, a speculator who "lost two fortunes and made three" speculating in currency markets.
Keynes was still up one fortune, if that should make everyone who ever lost money on an emu, a lahehouse, or a blog feel a little better too, as to bubbles being a part of capitalism.
Right now, America and Europe have something of a dilemma, in that by paying so much attention to Keynesian prescriptions over time, long run considerations are now colliding somewhat with short run considerations as to budgets, if that can be bridged so long as there are credible long rnn plans, if politically that creates a lot of hard work to be done.
As to the second aphorism, Keynes once said that "If you owe a man ten pounds, you are at his mercy. If you owe him a million pounds, he is at your mercy."
Clearly that is part of what happened as to making a Euro deal possible, and in a way offers lessons to the American government too.
Our creditors can't really just collapse us save in extremis, since they would lose too on average, if that isn't a free lunch either.
Europe and America spent many years developing social welfare and national security sytems that made sense to a point, if it was easy to promise things for the future that in fact would cost too much in taxes to be politically feasible or economically well-advised.
That was bound to create a collision, which is what the last four years have been about globally, as that was the basis for the prediction of the author that real estate would collapse in 2005.
That's the bad news.
The good news is that in an age of low barriers to entry to communication, and with the political technology called democracy, both Europe and America are well-positioned to adapt to the necessary changes, so long as everyone remembers one law of power, number 47: Know when to stop in victory.