In an ideal world, scientific discoveries would be independent of what scientists wanted to discover. A good researcher would begin with an idea, devise a method to test the idea, run the study as planned, and then decide based on the evidence whether the idea had been supported. Following this approach would lead us step-by-step toward a better understanding of nature.
Unfortunately, the life sciences are becoming increasingly estranged from this way of thinking. Early in their training, students learn that the quest for truth needs to be balanced against the more immediate pressure to "publish or perish". For a junior scientist to compete at securing a permanent academic position, her top priority must be to publish in journals with the greatest prestige and impact. If she survives to become a senior scientist, she's likely to then pass this lesson on to her own PhD students...