"If you want something done right do it yourself" is a nice idea in theory but one with limited applications. It is not possible for any successful institution to run without delegation of authority. And the bigger and more successful the organization the more partners that are needed and the more work that needs to be delegated. Many a potentially great organization withered and failed due to a 'do it yourself person' at the top who thought that only they could do it right. Even if true that they can do it better than others it is often better to let others do it. Great leaders have an intuitive sense of what they need "to do right" and what others can do instead. The truly great understand that often others can do it even more right than they. 
It is hard to imagine that one would not show up to their own wedding. Not because they get cold feet (that is strange enough) but rather because they prefer getting married through an agent. Yet it is precisely this scenario which serves as the basis of the Talmudic discussion on the concept of shlichut, of the parameters of agency in Jewish law. "A man may betroth his wife himself or through a messenger.[1]" (Kiddushin 41a)
While the Mishna is based on the principal of shelucho shel adam kmoto, the agent of a person is like the person themselves, the Gemara notes that the Mishna is actually teaching the principal of mitzva bo yoter mibeshulcho, that it is a greater mitzva to do something oneself rather than through a messenger. Otherwise there is little reason to teach that a man can betroth his wife himself - such is rather obvious.
The Gemara then quotes a view that the betrothal through an agent may be legally valid but it is forbidden to do so. "Rav Yehuda taught in the name of Rav: It is forbidden for a man to betroth a woman before he has 'seen'[2] her - perhaps he will see something distasteful in her and she will be loathsome to him and the Torah says "you shall love your neighbour as yourself."[3]
While agency is a given in the commercial world which we inhabit the rabbis of the Talmud were unsure of the Biblical source of agency. The Talmud posits four possible areas where the Torah either explicitly or implicitly allows agency, using these as a basis for agency in all areas; namely divorce, korban pesach, terumah and as our Mishna notes kiddushin, betrothal. 
That the Torah would single out the delivery of a get by an agent is most understandable. The agent reflects the separation and distance between husband and wife, presumably the reason they are getting divorced in the first place. Pesach is the time we join together as one nation and having an agent slaughter the korban pesach on behalf of others reflects this unity. In theory "all of Israel" could fulfill his or her obligation with the same animal - except no animal would be large enough.   
The entire institution of the kehuna is one based on the notion of agency. The kohanim serve as the agents of the Jewish people - in education, in service of G-d and as our civil servants tending to the religious needs of the people. It is most natural that the Torah would specify the notion of agency by terumah, the food that only a kohenand his family can eat. 
What is difficult to comprehend is why the Torah specifies the notion agency regarding marriage. As we have noted in the past the Torah discuses marriage in the context of divorce[4] and the Gemara says the same applies re agency. As agency works by divorce so too by marriage. But in this instance the Mishna is clear that agency is at best frowned upon. 
Marriage is the most intimate of relations and is one where agency has no place. It may be legal but is no basis for a marriage. And this message must begin with the kiddushin, as the couple commits to but has yet to begin their lives together. This may even be more crucial regarding the raising of children where the necessity of many couples to both work often means much of child-rearing is done by others.
The commentaries note that one fulfills the concept of mitzva bo yoter mibeshulcho, of doing the mitzva ourselves, even if one only does part of the mitzva. It is not practical for someone to do everything. Doing it right usually means doing it with others. But one must not delegate complete responsibility to others. 
We may have to, for example, delegate our responsibility of teaching our children to others but we must still spend a few minutes (or more) each week  learning with each of our children.
Agency is a given. But when to take advantage of such requires much wisdom. 
[1] While there may be little difference in our minds it is important to note that in Talmudic times the betrothal took place up to a year before the actual nuptials. With the couple still living apart until the nissuin it's not quite like appointing a messenger to stand in at the wedding itself.
[2] To "see" in this context means more than just to see. It also means to get to know. Only after having spent some time together is it truly possible to determine if one likes the person well enough to marry. This is especially true in an era such as ours with all too high divorce rates.
[3] While it is possible that one does get to know a woman and then appoint a messenger to carry out the actual betrothal apparently such a possibility was inconceivable to our Sages. The Mishna refers to a case where the couple are geographically separated, travel was difficult and a man sends a messenger to find him a wife. Even so (and let's recall that is how Yitzchak was married) our Sages discouraged and possibly forbade such.
[4]The Torah discusses divorce in the context of a prohibition of remarriage to one's former wife after she had been divorced from her second husband. The idea of experimenting and then deciding the first marriage wasn't so bad after all is one foreign to Judaism where marriage means a firm commitment. Mistakes happen but trial and error does not cut it._