Now here is the part most people miss. When you type a message, you see only your words. But AI sees much more. Your message is just one part of a larger context that gets sent every time. The app assembles this context behind the scenes before AI reads a single word from you.
At the top sits the system prompt, a set of hidden instructions written by the app developer. Below that is your full conversation history, every message you sent and every response AI gave, replayed from the beginning. Remember how we said AI forgets you the moment you leave? The memories the app saved from past conversations also get pasted into this context. Your latest message goes at the very bottom. AI reads all of this, top to bottom, every single time you hit send.
There is a catch. AI has a limited context window. Think of it as a fixed size page. Everything, the system prompt, conversation history, saved memories, and your message, all has to fit on that one page. As your conversation grows longer, older parts start getting pushed out or compressed. Important details you mentioned early in the chat can quietly disappear.
This leads to context rot. The longer the conversation, the more noise builds up. Your key instruction from 30 messages ago becomes a needle in a haystack. AI still reads everything in the context, but when there is too much, AI struggles to find and prioritize the parts that matter. There is another problem. AI pays the most attention to the beginning and end of the context. Information stuck in the middle gets overlooked. So even if your important instruction is still technically inside the context window, AI can miss it simply because it is buried in the middle of a long conversation. Researchers call this "lost in the middle."
This is why long conversations tend to go off track. The context got too noisy, AI lost focus, and the details that mattered slipped through.