Act as a senior software engineer with 10+ years of experience in [Python/JavaScript/Java]. Explain the difference between deep copy and shallow copy in [simple/technical] terms, using [real-world examples/code snippets] to illustrate the concept. Address common pitfalls developers face when choosing between the two, and provide best practices for when to use each. Ensure your explanation is clear enough for a [beginner/intermediate/advanced] programmer to understand.