In most modern music in 4/4 beats 2 and 4 are where the snare hits are and are usually referred to as the backbeat. Normally in 4/4 the 2 and 4 beat would not be accented, but the snare hits do just that. Where did this idea originate and why is it so important to accent 2 and 4?
Where did this idea originate? West Africa, then transplanted to the New World. It is a defining characteristic of African-American music, and all the styles of music that grew out of and were influenced by African-American music. It then spread to the rest of the world via the 20th-century music of the USA, Cuba, Brazil, Jamaica, and other nations with African descendants in the population who influenced the musical culture.