Just like a shark can smell blood from three miles away, it seems that men can smell a woman with low self esteem from even farther. It is apparently given off in pheromones and can be sensed by the males frontal lobe. (Don't Google that; I just made it up to sound smarter.)
Which brings me to the question: why do women have low self-esteem in the first place? Some have horrific adolescent experiences where grade school children have no registered emotion of hurting someone else's feelings and incessantly pick on someone's weight, height, etc. You would think that people grow out of that, right? Well some don't, and I can attest to that. I still am self conscious of my bust size, my smile, even the size of my feet. A better question still--do these grade school kids grow up physically but subconsciously remain those grade school adults, now with an agenda to pick on people? Whatever that agenda may be: financial class, jealously, or *gasp* because that person has low self-esteem themselves.
Another culprit is mass media as a whole. Companies and grass-roots movements are desperately trying to rid women all over of these screwed-up, innate paradigms that models are skinny, tall and possess one eating disorder or another. Other websites prove to show what some celebrities look like without Photoshop, make-up and other image-altering products. Is this helping young girls have better self-image and discern the real from the fake? The jury is still out on that one.
The obvious solution: love yourself. Point. Blank. Period. Whether you're a size 6 or 16. But until then, stay out of shark-infested waters.