The difference in skillset and mindset in a large organization vs a startup is pretty huge. A large organization values stability and conformity (your software must work within usually a much larger picture), whereas in a startup the organization values speed and flexibility (large business changes or new data may come in at any point). The challenge when coming in from a big company is convincing people you can "hack" it to get things done quickly while still bringing the monolith of process and organizational knowledge from the big company.