Fact or opinion.

Opinion or fact? Sometimes differentiate these two words is easy, for example, dogs are better than cats. It is clear that dogs do not have to be better than cats, it is just my opinion, but in other situations it is more difficult to distinguish whether it is an objective or subjective fact. If we put as an example "English people take longer to learn languages​​", certainly not all English people can only speak English, but this topic is generally used because, English is the best known language, and English people have not need to learn other languages ​​by force, however, a large number of English speakers can speak other languages ​​normally and this "fact" does not affect them.