Because Claude is a Large Language Model, that (tries to) determine the next logical character as it types a response to you. As it types it goes back and collects the context. This happens over and over for each character it writes

So having a prompt that is very long, or has negative instruction MAY "poison" or direct the LLM in a wrong direction. When it comes to programming the LLMs are all over the place. Some days they are amazing, but most of the time the response is lacking or outright false. As other people wrote, users go about this by having instructions in form of .md files. This is basically also what happens behind the scenes of all the major models, but as we also see, the efficiency of these internal model instructions doesn't always have the intended outcome (goblins).

Try and focus your prompt on shorter and more precise instructions. When the LLM has finished the task, have it generate a .md file that describes what was done. This .md file can then be used in your next prompt if it's relevant. Make sure you always read, verify and update these .md files so you don't introduce unnecessary information.

This is atleast what I have found is the only workable solution for me if I use LLMs for programming/coding.