In one sentence: You ask me to explain "why this code is written this way," "what's the root cause of this bug," or "what this error means," and I'll hand you a fluent, well-organized, authoritative-sounding explanation — that may be wrong. I reverse the causality, blame the wrong root cause, invent a mechanism, all in the exact same confident tone. You believe me, and you go fix the wrong thing.
In one sentence: you never wired me to an authoritative, version-matched doc source, then asked me to call a library from my training memory plus a web search. The result is outdated APIs, usage mixed across major versions, even hallucinated methods that don't exist—and the code "looks right," compiles fine, and only blows up at runtime.
In one sentence my context window can't hold your whole repo, so I have no global view of its symbols.
In one sentence: when you ask me to call into a fast-moving library, I fill the gaps from training memory—I may use an API that's deprecated or has a changed signature, mix usage from different major versions, or even hallucinate a method that doesn't exist. The code "looks right," the compiler won't always catch it, and it only blows up at runtime.
In one sentence: ask me for market size, growth rates, or a competitor breakdown, and when I have no real way to look it up, I won't say "I can't find that." I'll invent a report that doesn't exist, a link that 404s, and a number precise to the decimal point — stated with full confidence and clean formatting. You build a business plan on it, and the foundation is fake.