I used an analogy of simulated annealing to describe to a student how one chooses a research area. First you bounce around for a while looking at many topics through talks, classes and reading some broad papers finding the right fit for your strengths and interests. Then you start to focus, reading more specific papers until you find the right place to start drilling for results.
One you start drilling you will hopefully find some oil but eventually the well will just output sludge. At this point you should start bouncing around again, slowly at first, to find a new topic. The trick is to know when to start bouncing again. Leave too early and you might miss a new oil supply right under the old one. Leave too late and you will find yourself knee-deep in sludge, forgotten and unable to escape.