We can roughly divide our lives into two elements: the times of giving out and the times of taking in (there are also moments of both, as there is no exclusivity). These elements do not fall into to linear wholes (a time of taking in may be followed by giving out, then again by taking in) and they have no set limit to their duration or precise structure. But there are fundamental to a life well lived.
Early lives are all about taking in. Infants and young children have very little they can give and very little capacity with which to give. As we grow in age we learn the capacity to give and slowly gain things to give. In our childhoods we are fed with knowledge and love; discovering how to truly be human; how to have real, powerful relationships, gaining an appreciation for others. Our parents, teachers, siblings, friends, all pour into us from the wealth they have accumulated, filling our persons with everything we need for life.
This time is at the heart of all education and particularly college, at least in the traditional sense. The university was the place that formed the full man, teaching him not simply knowledge (or what can often pass for knowledge) but how to respect others (hint: it does not involve beer pong), how to be a true patriot (which does not involve painting the American flag on your belly), how to treat woman (whistling not included), and so forth. The man or woman who truly graduates from the university has not simply a degree declaring his or her competence in a given field, but has the wherewithal to be truly human. (A similar end should be accomplished elsewhere for those for whom the university is not the right choice).
Once one has gained this tool set (via the university or, more often today, the several years following it when one cannot live on beer and ramen) there is the transition from taking in to giving out. The skills and wisdom imparted to a youth are then his to impart to others; as they say, love is that which grows when given away.
This is (surprise, surprise) particularly evident in vocations. The first steps of any vocation should be discernment and formation, the former melding into the later. In discernment you receive the views and knowledge of many, drawing in all that is available. Once it transitions to formation the knowledge and wisdom becomes more focused, and the young man takes in many skills particularly suited to his vocation.
The period of formation ends when one enters into a vocation (though formation itself should be ongoing) and the focus transitions to that of giving out. Both Matrimony and Holy Orders are sacraments “oriented toward the salvation of others” (CCC 1534); one receives this so that he may give out to others. It is similar with any vocation, even when there is no sacrament there. Entering into one’s vocation brings about a profound change in the orientation of that part of life; a man is suddenly responsible to his wife, and a woman to her husband. A priest is responsible to his parish and a sister to her community. We are called then to focus no longer on taking in, but henceforth to give out all that we have gained so that others might truly live.