The announcement of a major shareholder selling a significant amount of stock typically leads to negative sentiment among investors, as it can imply a lack of confidence in the company's future prospects or an expectation of lower prices ahead. Additionally, the increase in available shares can lead to dilution and downward pressure on the stock price. Squarespace not receiving any proceeds from the sale further exacerbates the negative impact, as there is no direct financial benefit to the company from this transaction.