Just as a fruit contains two elements, its edible portion and its seed, so the consequence of each of our actions is twofold. One element of the consequence of each action is the pleasure or pain that we must sooner or later experience as a result of it. This element is like the edible portion of a fruit. The other element, which is like the seed contained within that fruit, is the resulting karma-vasana, the tendency or inclination to do that same action again.
That is, our karmas or actions are habit forming. The more we indulge in any particular type of action, the more we will generate and nourish a corresponding vasana, an inclination or liking that will impel us to do the same type of action again.
verse 38 of Ulladu Narpadu
http://happinessofbeing.blogspot.com/2007/07/actions-or-karmas-are-like-seeds.html