The case is often wrongly summed up as “McDonald's lost the Big Mac”. That is inaccurate. The BIG MAC trade mark remains protected in the European Union for meat-based sandwiches — that is, for the product itself.
What Supermac's obtained concerns the extent of the protection: the trade mark had been registered for a broad scope — including chicken-based products and restaurant services — which McDonald's failed to show it actually used. And European law is clear: it is for the proprietor to prove genuine use of its trade mark, and the lack of proof entails revocation.
That is the procedural lesson. A major brand loses rights not because a competitor demonstrates something, but because it did not produce the documents it was asked for.