"Sure as eggs is eggs" is a popular phrase that is usually used to express confidence in a particular outcome, event or situation. However, if you're looking to switch up your vocabulary and find alternative ways to convey the same degree of certainty, there are plenty of suitable synonyms to choose from. For example, "without a doubt," "certain as day," "absolutely," "undoubtedly," "positively," "definitely," "unquestionably," and "beyond any shadow of a doubt" are all great alternatives. So, don't restrict yourself to just one phrase when expressing unwavering confidence in something. Experiment with these synonyms and add some color and variety to your language!