I use Claude Code a lot and GPT 5.5 as well, and find that they are simultaneously extremely useful and also fall into common poor-performance basins. For example, writing performance -- perhaps my biggest issue with them is writing style -- such as well documented stylistic tics (em-dash, it's not x it's y), less commented stylistic tics ("the honest framing", "the earned XYZ"), cryptic and coined jargon, overabbreviation and sentences replaces by arrow constructions (this -> that -> this other thing), poor understanding of the audience's familiarity with the analysis, grandiose framings, as well as explaining things in a motivated intuitive way.

Another common trap is overengineering analytical solutions, or failing to consider limitations or common failure modes unless I point them out.

Would love to hear what other failure modes you've navigated, and see the prompts (system or otherwise), skills, and other techniques that you all have found helpful to get better performance and more usable output out of these tools.