That was my feeling back when 'we made this site in 3 days using Ruby on Rails!' was all the rage.

Frequently it was really 90% of an app. I like for things to be polished, have no error messages, handle all different types of input gracefully, and so on. The sites made in 3 days never did that. It's like 'the first 90% took 3 days, the last 10% took 3 weeks'. Details are difficult.

But then, that's where cutting out features or releasing an MVP comes in. If it's a really slim product, it's possible to make something usable, at least, in 24 hours. But why not just take a week or two and make it really good? There's no rush.