It's not just about confidence. It's also about the speed you can use/refactor the code. Suggestions, type information on hover and instant feedback if you forgot, used wrong order or type, misspelled or simply don't remember exactly signatures or auto generated documentation means a lot when writing code. You can move much faster when working on typed code. Nobody ever claimed that types are replacement for tests. It just means that your tests don't require obvious clutter anymore, you can focus on more complex/important test cases to cover.