It looks like you entered a fragment ("why did") that’s open to many interpretations. If you’d like, I can help clarify or complete it in several common contexts. Here are a few possibilities and concise explanations:

• Why did you do that? — A question about someone’s action or decision, often probing motive or reasoning.
• Why did I do that? — A reflective or self-questioning line, sometimes used in introspection or self-critique.
• Why did this happen? — A query about cause or explanation for an event or outcome.

If you can share a bit more about what you’re aiming for (e.g., a sentence, a dialogue, a song title, or a specific situation), I’ll tailor the explanation or rewrite precisely.