Imagine that instead of setting out to invent a better lightbulb, Thomas Edison had announced his intention to invent a light-emitting diode that you could use to illuminate your kitchen. This isn't completely far-fetched: the first examples of light-emitting diodes (LEDs) began to appear as early as 1907. But it wasn't until the 1960's and 70's that useful, visible-spectrum LEDs began to appear, and LEDs haven't been used to light kitchens until very recently. Thomas Edison, had he set out to make a useful, household LED, would have been doomed to failure beacause it would be years before basic science made the necessary technologies possible.
When Richard Nixon declared the conquest of cancer "a national crusade" in 1971, cancer researchers were inevitably set up to be viewed as failures. Although at the time the recent molecular biology revolution led people to think that disease conquest was just around the corner, now we can look back and see that the War on Cancer had no hope of achieving its goals in the 1970's. Scientists are being punished for that hubris now, in the form of misguided news pieces such as Newsweek's current exposé: "We Fought Cancer...And Cancer Won".