On one hand reading hacker news left me with the impression that creating a business is incredibly difficult with so many things to get right, and on the other

On one hand reading hacker news left me with the impression that creating a business is incredibly difficult with so many things to get right, and on the other there are companies like this successfully raising money and growing, I'm really puzzled. Sure they are not sustainable but are investors still fooled by this? By my limited experience in the B2B space they are usually quite smart and know how to do a serious due diligence Edit: I understand the investors could have taken a conscious high risk bet on an unsustainable business model, but how it comes the founding team didn't raise any red flag to the investors before?