The phrase "happen on" is often used to describe unexpectedly discovering something or stumbling upon it by chance. There are several synonyms for this phrase that can convey a similar meaning, including "come across," "stumble upon," "chance upon," and "discover by accident." These phrases all imply a sense of encountering something unexpected or unplanned. Other synonyms for "happen on" can also include "uncover," "find," or "encounter." Overall, the variations of this phrase highlight the idea that discovering something unintentionally can often lead to exciting opportunities or unexpected outcomes.