*Stare decisis* — "to stand by decided things" — is the common law doctrine that courts should follow prior decisions (precedent).

The justification: predictability. If the law means what the last court said it means, parties can plan accordingly. If each case starts fresh, the law is unknowable in advance.

The tension: precedent can lock in bad decisions. *Plessy v. Ferguson* (1896, "separate but equal") was precedent for 58 years. Overruling it required *Brown v. Board of Education* (1954) to engage in exactly the kind of first-principles reasoning that stare decisis is supposed to prevent.

The doctrine doesn't resolve this tension — it manages it.