Blunder upon is a phrase that refers to stumbling upon something, often by accident or chance. The antonyms for this phrase would be to deliberately seek out or plan for something. This could include carefully researching or planning to discover something, rather than simply stumbling upon it by chance. Other antonyms could include words or phrases that describe more intentional and deliberate actions, such as carefully investigating or thoroughly preparing. While blundering upon something can be exciting and unpredictable, intentionally seeking out information or experiences can be just as fulfilling and rewarding.