Original link: Expert Generalists / Martin Fowler.
On the surface this looks like BS. If the human brains capacity is modeled as a rectangle, then it can be either wide and low or narrow and tall or something in between. But if one dimension increase then another dimension decrease. Tradeoff.
But I suspect that they are really trying to promote the value of generalists in an industry focused on specialists (job ads looking for an ASP.NET Core developer with deeep knowledge about Razor and EF Core as an example). Not in the "full stack developer" sense, but more cross technology and cross domain.