No, sometimes courts will overrule their past decisions. The law evolves and changes over time due to changes in societal attitudes, the composition of the court and other factors. The most classic example was when the U.S. Supreme Court in Brown v. Board of Education (1954) overruled the “separate but equal” doctrine in Plessy v. Ferguson (1896). The Court in Brown determined that segregated public schools violated the Equal Protection Clause, while the Court in Plessy had upheld a Louisiana law mandating separate railroad travel for different races.

More recently, the U.S. Supreme Court in Roper v. Simmons (2005) ruled that juvenile murders cannot be executed, because that would violate the Eighth Amendment against cruel and unusual punishment. The Court focused on the fact that juveniles have less appreciation and cannot control their behavior as much as adults. The Court overruled its prior decision in Stanford v. Kentucky (1989).

Perhaps the quickest reversal occurred in the 1943 decision West Virginia Board of Education v. Barnette (1943) where the justices reversed the decision in Minersville School District v. Gobitis (1940). In Barnette, the Court invalidated a West Virginia flag salute law that forced public school students to stand, recite the Pledge of Allegiance and salute the flag. In Gobitis, the Court had upheld a similar Pennsylvania law.