The two central and most important tefillot of Yom Kippur are the yud gimmel middot harachamim, the 13 Attributes of mercy, and the al chets, the listing of the sins we (may have) committed during the previous year. The former focus on G-d while the latter focus on man. 
And the Lord passed by before him, and proclaimed' (Shemot 34:6): Rav Yochanan said: Were it not written in the text, it would be impossible for us to say such a thing; this verse teaches us that the Holy One drew His talit round Him like a shaliach tzibbur, and showed Moshe the order of prayer. He said to him: Whenever Israel sins, let them carry out this service before Me, and I will forgive them" (Rosh Hashanah 17b). 
If the 13 Attributes are G-d talking and teaching us how to attain atonement the al chets is the mechanism through which we acknowledge our own sins. Like many of our prayers - especially at this time of year - it is a (double) alphabetic acrostic. In other words it is a form of poetry in which form may be as important as content. 
Al chet shechatanu lefanecha b’onesh, u'vertzon, for the sin we have committed before you, against our will and willingly”. So begins the first of the 22 stanzas of a litany of sins. Yet the first sin mentioned seems to make little sense. In fact it is not a sin at all. “Ones Rachamana patrei, G-d excuses those who are forced (to sin)”. While we must admit our guilt for those sins done of our own choosing there is no such guilt to admit for sins we were compelled to do. Of all the possible “sins” with which we may begin why start with a “non-sin”. 
We humans sin and most of us sin a lot, sinning in a variety of ways every day. Yet most of us (I hope) don’t truly want to sin. We want to do the “right and the good” but the pressures of life get in the way. We begin our confession by beseeching G-d to consider all of our sins from A to Z  to be as those done under duress, as a result of the difficult situations we often find ourselves, and thus we should not be held responsible. 
The mystics teach that Yom Kippur is the second most important day of the year - following that of Purim. Yom Kippurim as it is called in the Torah, is Yom K’ Purim, a day like - but not quite like Purim. In explaining this most enigmatic teaching Rav Soloveitchik notes that our claim to forgiveness is based on Purim. Purim means lots and it is our lot in life - given to us by G-d - that leads us to sin. Our lot is to be living in the 21st century, in a society that is sexually promiscuous, where personal autonomy knows no limits, where the financial pressures are enormous, where the allure of technology is seen to be more exciting than study, where gossip is an art and public discussion of religion is frowned upon. Is it any wonder that we sin? What G-d, do you expect us to do? Had you placed us in the shetel where Torah permeated life and the temptations to sin were relatively minimal we would be much different. We begin by telling G-d that sinning is something we can’t really be held responsible for.  Our sins are forced upon us so please do not hold us responsible for them. 
“Rav Chiyah the son of Abba said in the name of Rav Yochanan: It [the evil inclination- given to us by G-d] can be compared to a father who takes his small son, bathes him, douses him with perfume, combs his hair, dresses him up in his finest accoutrements, feeds him, gives him drink, places a bag of money around his neck, and then goes off and puts his son at the front door of a brothel. What can the boy do that he not sin?”
Yet at the same time we can offer an opposing perspective. We often try to excuse our sins by blaming others, by saying we had no choice. Yet we make our own choices and what may appear forced is often just a bad choice we make. We may blame others but it is we who are at fault. Furthermore even when we are no longer in control of events and forced to act in ways we were not meant to, such may be the result of bad choices made in the past. We may truly be forced now but we put ourselves in this position and “being forced” can not fully absolve us. “In the path that man desires, there he will be led.”
While these two approaches seem contradictory - and they probably are - they are both true. We are responsible for the choices we make but G-d can make those choices so difficult that we are not fully to blame. If we can say such, it is both G-d and man who are responsible for our sins - or at least such is our plea for forgiveness. 

G-d in revealing the 13 Attributes to Moshe and the Jewish people informs us that He is a merciful and kind G-d. May that mercy and kindness be manifest to us, our families the Jewish people and the world at large. Gemar Chatima Tova!