Spelling mistakes occur when words are written incorrectly, often due to typographical errors, phonetic confusion, or lack of knowledge about the correct spelling. These errors can happen in any form of writing, from casual texts to formal documents, and can affect the clarity and professionalism of the communication. Common causes of spelling mistakes include homophones, where words sound the same but are spelled differently, and typos, which are accidental keystrokes. Tools like spell checkers can help identify and correct these errors, but it's still important for writers to proofread their work to ensure accuracy.