The IT consulting firm will tell you they have experience with literally everything. They’ll dig up a case study from one of their 400 offices somewhere, claiming to be experts on whatever the topic is. Meanwhile, in actuality, your project will be staffed with a team of 24 year old kids where this is their first assignment. And it doesn’t matter anyways, because the people who worked on the original case study are long gone and would never communicate with other offices even if still around.
Meanwhile at the big company, you’ll have the opposite problem. A team of people with decades of experience, but who don’t really know anything about anything other than how to make their corporate machine not fire them. They’ll think they know what they want, and will confidently tell you…but in actuality, these people have zero understanding of technology or even how their business runs. And who can blame them, they’ve spent a 30 year career not doing or risking anything specifically, so its hard to learn how anything works with no feedback loop.
It then becomes a delicate dance, can the consulting team learn how to do the thing they sold the client fast enough, before the client does their best to try to ruin the project out of sheer hubris and incompetence.
This case is famous for being one where the dance went so bad it became a meme.