Why does my AI agent ignore my instructions?

Usually because the instructions are aspirational rather than checkable. 'Be careful with quality' gives the model nothing to verify; 'do not commit unless tests pass' is a gate it can honor. Second cause: rationalization — under pressure the model convinces itself this case is the exception, so durable instruction files name the excuses in advance ('this is too simple to need a test' is listed and forbidden). Third: instruction dilution in long sessions; put hard rules in persistent persona/skill files, not one-off messages, and keep them short enough to stay salient.