Astronomy as a profession is hyper-specialized.  What do you study-- planets, stars, galaxies, clusters, cosmology? Oh, if only it were that simple.  Say you study stars.  It doesn't stop there!

If stars, what wavelength?  There's radio, IR, optical, UV, X-ray, gamma-ray, multi-wavelength work.  Oh, you study X-ray emission from stars?

What kind of X-ray stars-- single, binaries, compact objects, remnants?  You're into binaries?

What kind of binary star X-ray emission-- coronal, accretion disk, Roche lobe overflow?

By the time you pin yourself down as an expert on X-ray emission due to accretion from Roche lobe overflow in equal mass occulting semi-detached double stars, you're neglecting over 99% of astronomy. But for that specific topic, you rule!  Woo!

Alex, the daytime astronomer