Since you have experience in both, what would you say the key differences are between working in an established, structured firm (such as Goldman Sachs) and working in the world of start-ups?

I think you might have answered your own question, the operative concept being “Structure.” Start-ups do not have this by the vary nature of what they are. I think for one to think about working for a start-up, they have to enjoy unstructured environments. Ultimately what you learn is how to create processes, systems, products at scale. Conversely a large company, like a Goldman Sachs is a great training ground before you venture into the start-up world b/c you can now have a skillset to add (so you are a structure enabling element). Thanks for asking.