add why section

Author: le0pard

README.md

@@ -1,6 +1,18 @@
 # JsonMend [![Ruby Checks](https://github.com/le0pard/json_mend/actions/workflows/main.yml/badge.svg)](https://github.com/le0pard/json_mend/actions/workflows/main.yml)
 
-`JsonMend` is a robust Ruby gem designed to repair broken or malformed JSON strings. It is specifically optimized to handle common errors found in JSON generated by Large Language Models (LLMs), such as missing quotes, trailing commas, unescaped characters, and stray comments.
+`JsonMend` is a robust Ruby gem designed to repair broken or malformed JSON strings. It is specifically optimized to handle common errors found in JSON generated by Large Language Models (LLMs), such as missing quotes, trailing commas, unescaped characters, and stray comments
+
+# Why?
+
+Integrating Large Language Models (LLMs) into software workflows often requires structured data output. While prompting an LLM to "return JSON" is a common pattern, models are probabilistic text generators, not strict serialization engines. They frequently treat JSON syntax as a loose suggestion rather than a rigid standard.
+
+Standard `JSON.parse` is fragile when facing the chaotic output of an LLM. Common failure modes include:
+
+- **Hallucinated Syntax**: LLMs often include trailing commas, code comments (`//` or `#`), single quotes, or Python-style literals (`True`, `None`) that break standard JSON parsers
+- **"Chatty" Wrappers**: Models frequently wrap JSON in Markdown code blocks (`json ...`) or include conversational preambles ("Here is the data you requested: ..."), turning valid data into invalid syntax errors
+- **Truncation**: JSON is verbose. Output limits often cut off the response mid-stream, leaving unclosed brackets and braces
+
+`JsonMend` acts as a middleware layer between the messy text output of an LLM and your Ruby application. It aggressively parses, cleans, and repairs the raw string—handling truncation, stripping garbage text, and normalizing syntax—to ensure you get usable structured data instead of a `JSON::ParserError`
 
 ## Features