The purpose of this paper is to explore the nature of eros in relation to a sense of lack in Plato's "Symposium." It starts from a sketch of the idea of fulfilment that is often found in the contemporary culture, especially when it is connected to the sense of a good life. The term 'fulfill', consisting of 'fill' and 'full', implies a sense a lack and an action of filling. Filling the lack to the full is the image that is often entertained when a good life, or a good education, is considered. The paper examines the similar image contained in Plato's "Symposium," where lack is assumed as the precondition for love. One of the aims for love is to fill the lack; that is, to obtain the object of love. Three speeches in the "Symposium," given by Aristophanes, Socrates and Alcibiades, will be discussed in turn. In doing so, three issues, in particular, will be discussed: the sense of lack, the object of love, and the aim for love. I suggest that instead of a straightforward solution to the predicament of love, a better way of understanding Plato's account of love through the three speeches is by understanding it as a dilemma, an approach taken by Martha Nussbaum. Nussbaum argues for Plato's hesitation in following Socrates' program of the ascent of love, in which the 'lack-filling' is guaranteed. The teacher's role is thus understood in two different ways. It is on the one hand, as the bridge between student and knowledge, and on the other, the revealer of the values of lack. The paper finally adopts a Lacanian idea of ontological lack to supplement Nussbaum's argument, taking up the often neglected values of lack in the Symposium, and its implication for education.