Many people have sought to answer this question in so many ways but as expected it is never answered to the satisfaction of all. The apologist's deny any contradictions and are working hard to try to reconcile those contradictions; while the non-believers such as myself see these contradictions as proof that the gospel story cannot be trusted as historical or factual.
I've thought about this question for quite some time; and have come up with what I believe is a simple answer to why the synoptic gospels as well as the gospel according to John are so different from each other and disagree on the details regarding the life of Jesus. First and foremost is the fact that none of the gospels are first hand accounts of the events that they describe. Second, none of the authors of those gospels are actually the persons whose names are attached to the documents. Until about the mid second century the gospels were all recognized to be anonymous works, and their authors because of this till this day remain unknown.
If you take into consideration that the gospels were entirely based on oral traditions and not historical facts, but rather tales or shall we call them what they really are? Folktales. The online Mirriam Webster dictionary defines a folktale as': a characteristically anonymous, timeless, and placeless tale circulated orally among a people.' http://www.merriam-webster.com/dictionary/folktale Our gospels definitely meet all of the criteria of a folktale as defined by Merriam Webster.
One last thing to consider is that oral stories tend to change and evolve with the telling. As time goes by they are usually embellished to convey a certain teaching or in the case of the gospels; the many doctrines that have been derived from the many tales that they are composed of. If there are any historical facts in the gospel tales about Jesus it is almost certain that they have been greatly exaggerated as time has passed and are not the same tales that were being told in the beginning. I am pretty sure that what we have is the greatly exaggerated tales of the anonymous authors of those gospels.
This last fact is made evident from the various ways in which the tale is told by the various authors who are telling them. If we include the gospel of John among the synoptic gospels what we are really reading in them is four different tales told by four different authors and their interpretation of the oral traditions as they have received them. Taking this into consideration will help make sense out of why there are so many discrepancies in the tales about Jesus.
The authors of the gospels are four different authors with four different tales to tell based on their own individual interpretation of the tales that they have received orally most likely from their family or friends. Out of these four tales the authors have all come up with their own doctrinal beliefs based on what they have learned and how they have learned it. If you study the New Testament carefully you will be able to see the various doctrines within the texts themselves. Even back then the church was divided on doctrinal matters regarding the end times, resurrection, the role of women in the church etc.
In closing I think that this simple idea about the gospels in particular can also be extended to the entire bible as a whole. It helps explain why we have so many contradictions in the scriptures and why they cannot be reconciled without going through some ridiculous mental gymnastics to try and make sense out of nonsense. Think of it as being similar to having four psychiatrists write on the same subject separately and then putting all of their works together into one book. This is what happened with the gospels and the bible as a whole, I am pretty sure that the various authors of the scriptures had no idea that one day all of their works would be put together with those of other writers both in agreement and at odds with their beliefs.