Walter Landor was a brand design legend and the founder of Landor Associates mostly known for designing the FedEx logo (among many others). It was a product of a long process of creating and reviewing over 200 designs.
Only one person at the logo presentation spotted the ‘secret’ within the logo. That’s why that person was the CEO of FedEx I suppose.
To offer a brand mark that offers more in later viewings is a wonderful thing. A logo you see many times, before one day you look again and see something… extra.