As a longtime viewer of the show, I did manage to pick a few recurring themes and lessons from the show:
-Beware your less attractive/successful/popular best friend, as they will likely kill you. ("Stand Up and Holler", "Andy in C Minor", "Pin Up Girl", "The Crossing", "Hoodrats")
-Take care when you demonstrate talent at a particular sport or art form, as this may get you killed... ("Disco Inferno", "Shuffle, Ball Change", "Triple Threat", "Hoodrats")
...but the same can be said of trying to quit. ("Colors", "Superstar", "Stand Up and Holler", "Soul", "Dead Heat", "Forensics")
-Railings are the most useless invention known to man. The slightest nudge will send someone careening over them, physics be damned. ("The War at Home", "Torn", "The Crossing").
-If you absolutely MUST tell an acquaintance how pathetic they are, it's probably not a good idea to do it while you're standing someplace high, or while they're holding a gun. ("Schadenfreude", "8:03", "The Crossing")
-If you find out someone you know is doing something illegal or immoral, it's best to go to the authorities, rather than confronting them directly. ("Bad Night", "Frank's Best", "True Calling", "The Brush Man", "Mind Games", "Chinatown")
-Baseball players being beaten to death with their own bats has been a occupational hazard in Philly for decades. ("A Time to Hate", "Colors", "Stealing Home").
-High school students being mowed down by faculty members at their prom was apparently a common occurrence in the 1980's. ("Family", "Almost Paradise")
-Men are racist, women are not. ("Strange Fruit", "Family 8108", "Wednesday's Women")
-Do not turn your back on someone with a gun, no matter how certain you are that they won't shoot you. ("November 22nd", "Chinatown", "The Runaway Bunny")
-Spouses of returning vets are notorious for being unfaithful... ("Honor", "The War at Home", "The Good Soldier")
...in fact, victim's spouses in general are usually cheaters. ("Schadenfreude", "The Good Death", "Witness Protection")
-Older siblings kill younger siblings, never the other way around. ("It's Raining Men", "Time to Crime", "Revolution", "Shuffle Ball, Change", "Wunderkind", "Lotto Fever", "Chinatown")
-Conversely, younger siblings are more likely provide leads to reopen their older siblings' case. ("Superstar", "Knuckle Up", "Running Around", "Wednesday's Women")