Probably Google's biggest failure ever was to recognize they've already had a social network: Gmail.
The social network they were not developing well was YouTube. Eventually, they figured it out, and it's estimated YouTube would be worth $550B as a standalone business today [2].
[1] https://en.wikipedia.org/wiki/Google_Buzz
[2] https://variety.com/2025/digital/news/youtube-valuation-wort...