styling order is counter-intuitive

so, i'd like to understand (before proposing a change) to why css styling
does not follow the order in which classes are added to an element but
instead an element gets styled in the order classes are found in the
stylesheet.
if there's a webpage with an explanation i'd like to read it, so if someone
could point me there that would be great.
i find it very counter-intuitive, not to apply styles in the order they are
added to an element, but i'm sure there's a reason..