Longitudinal studies are a mixed blessing for any up-and-coming researcher. You have to wait so long that the world seems to pass you by, and when you finally publish, your results are often drowned out by more fashionable controversies. Worse, you might die before you actually get any interesting results. Yet, if you can last the course, you get the last laugh, because the long view of human development is the most informative, since each person is their historical control. The cross-sectional dross is revealed to be a mess of confounding variables. The true strong light is longitude.
Below is a short video about the Study of Mathematically Precocious Youth, now 45 years old. It is a university production, with an upbeat American tone. If that proves too much for you, watch a Scandinavian murder mystery instead.