Advanced greedy problems often have subtle traps:
Tiebreaking matters.: In some problems, how you break ties changes the answer.
Greedy criterion depends on subproblem.: Create Maximum Number uses different greedy criteria at different stages.
Proof is not obvious.: Patching Array's doubling insight requires careful analysis.
Combine multiple techniques.: Some problems need greedy + heap + sorting together. If a greedy solution feels too simple, test edge cases carefully. The devil is in the details.