What are the most common scenarios or causes that lead to an 'unexpected indent' error?

Common causes include: 1. **Accidental Indentation:** Adding extra spaces or tabs at the beginning of a line unintentionally. 2. **Incorrect Block Structure:** Indenting a line when it should be at the same level as the previous block (e.g., an `else` statement incorrectly indented after an `if` block). 3. **Mixing Tabs and Spaces:** Python treats tabs and spaces differently. If you use tabs for some indents and spaces for others within the same file or even the same block, it can confuse the interpreter and lead to this error. 4. **Copy-Pasting Code:** When copying code from another source, inconsistent indentation or hidden characters can be introduced. 5. **Leading Whitespace on Blank Lines:** While less common, sometimes leading whitespace on a blank line can indirectly contribute if it affects how an editor's auto-indentation behaves on subsequent lines.