I've heard this on several occasions and I think it is true if we're spending too much of our time on them. It might not be true for some people, but then, how do they decide it isn't true for them? How do we recognise that we're spending too much time asking the wrong questions, and once we recognise that, what's the best way to proceed?
I think our competitive society clearly rewards asking productive questions. We ask them all the time, and we get answers. So I see no indication that not enough productive questions are being asked by the population at large. In bulk, we are, by many measures, overproducing, in the sense that our production rate undercuts the value of labor and threatens us with fears that the institutions it supports may not be sustainable. So purposely increasing productiveness seems, well, almost counterproductive.
At the same time, we occasionally see huge returns from the solution of a hard-to-answer question. Turing's work, although very hard and abstract with a completely unhelpful negative result, also showed in detail for the first time how much computing can be simplified and automated, and basically gave birth to computing as a discipline. In all of the sciences, the level of resources we have traditionally heaped on hard problems has consistently paid off big, if not often.
So I think this question is based on a combination of errors of perception -- that good things are not worth waiting for, and that one must 'make hay while the sun shines' no matter how much hay one might have in storage.