explanation 1)
most girls/womens' hobby is it to go shopping so that they naturally have many different clothes. and if you've got options then you try to go for the most appropriate one... if you can choose between 20 cars/girls/bananas or whatever then you're obviously gonna try to find the best- depending on things like event or personal mood etc...
another magical word is combination: 8 pullovers, 25 shirts, 7 trousers, 12 pair of shoes and 4 jackets/coats makes a merely uncountable number of possibilities of combination- and trying them all takes a sh*tload of time- if there's a mathematic-skilled person in da house s/he may tell us how many possibilities there are in my example

explanation 2)
(a darwinistic/evolutionary theory i came up with while watching students in graz biggest students' bar)
struggle for existence!
it is the most important aim for every living being in a population to secure the existence of its genes within the next generation. but to reach that, a being of the same race with the opposite sex is needed. the fact that the descendent (ergo child ) has got 50% of the genes from the male and 50% of the genes from the female part includes the fear of either that the 50% of the genes which the descendent gets from the opposite sexual partner are of minor quality. therefore it is necessary to get the (appearantly) best being available of the opposite sex. due to the big competition among your own sex and due to the very small quantity of good specimen, it is logical that one tries to get advantage in selection. for animals it works that way that the men fight and the strongest (the appearantly best) is allowed to pass on his genes by coiting with the female specimen. with humans it works that way that girls try to cover up their least advantageous parts and push (pun intended) their more adventageous parts so that she in advantage of her rivals. and with some females that lasts hours


p.s.: though i've written this in a merely funny way and though this may sound a bit strange i'm absolutely serious with what i've just written!!!!