What I recall about my Federal Courts class in law school was that it was (1) very difficult, and (2) very confusing. And I tried. Hard. (I ended up doing just fine, but still.)
I say that because I had a similar reaction to the two Ninth Circuit opinions published today, both of which directly involved various complicated doctrines that we discussed at length in Federal Courts.
The first of today's opinions involves Younger abstention alongside constitutional ripeness doctrines in the context of a federal First Amendment challenge to medical disciplinary proceedings brought against various Washington state doctors who published misleading information about COVID during the pandemic. Yikes. Complicated complicated complicated. (But, ultimately, yes, the federal courts abstain over many of the claims and the rest are unripe).
The second opinion involves yet another abstention doctrine -- this time, Colorado River -- and how it in turn applies to appellate deadlines under Rule 58(c); do you have to file an appeal immediately under the collateral order doctrine, or can you wait until the denial of a motion to vacate the stay, and in either event, when does the appellate clock start ticking in the context of a "text-only" (i.e., no PDF attachment) minute order from the district court? Yet more multifaceted and complicated stuff. (Short answer, by the way: You must appeal immediately.)
In short, my head hurts today in somewhat the same fashion as it did 35 years ago as a 2L in law school.