てからでないと

てからでないと expresses a strict condition: something cannot be done or the situation won’t occur unless you first complete a preceding action. It emphasizes that a prerequisite action must be completed before the main action or outcome. This construction is common in explanations of Rules, processes, or requirements in everyday life, work, and study. It often conveys a sense of necessity or constraint, sometimes with a nuance of warning or impatience when the prerequisite isn’t met.