Optimism I believe does have a very positive effect on both productivity of the people and how much they love working in a place. But in my experience overdoing it might make your employees start developing this "This does not make sense at all, why are these people living in dreams?" mindset. From chats I had, I could feel some of my colleagues also had a hesitation towards the goals etc. It was interesting to see people become frustrated especially if they have been used to being slightly pessimistic and cautious due to their background(title(Finance background), nationality(mostly non-US and UK people) etc.)

Overall very nice article though, I do believe moving fast in hiring is the most yield/effort you can do to hire great people. Best companies I worked for(above one included) moved extremely fast in hiring, worst take 2-3 weeks just to reply to an email let alone scheduling an onsite. Wish decision makers in recruiting knew this.

p.s. love the Stripe Docs and Technical blog posts, this one specifically was very informative: https://stripe.com/en-de/blog/api-versioning