Neapolitan Mastiffs, as a breed, are extremely intelligent dogs with a tendency to be independent thinkers. They learn quickly, which is both good and bad, since this guardian breed needs extensive proper socialization to learn to accept strangers, especially within the home; without proper early socialization and training, these dogs are likely to become aggressive towards strangers and unfamiliar dogs.
Neapolitans must be well socialized with people (especially children), as they are large, powerful dogs and do not always know their own strength. Additionally, young children have young friends, and even with extensive socialization and training, Neapolitans will be wary of strangers and protective of their family, which can be disastrous for small children. Most of the time, they will protect their owners with their lives.