Because the brush is small and round, it grabs onto each lash, giving you just the right amount of curl and definition, section by section.
It would take a little bit of getting used to using it on yourself, as its very different to "usual" mascara, but it is by far the best mascara I have ever, ever used. It perfectly coats every lash and gives a nice curl, as you can work in small precise sections, pushing the lashes up and outwards as you go.
Also available in a waterproof formula. You can get it at Givenchy.