I actually wrote my introduction first because I know that I am not good with writing. So, doing it first gives me the chance to keep on improving it until it is good. Yes, you are right that, some times, we do not know the whole picture yet.. so as I went along, I changed it here and there a number of times, until everything is clear. Not only it was a good practice for me, it is also an exercise in understanding the sequence of my experiments and the overall findings. Yes, it is true that doing it last will make it a bit of a rush. I agree.
During the Middle Ages in Europe and the Middle East there was much armed conflict between Christians and Muslims. Christians called these conflicts the Crusades because they were fighting under the sign of the cross to save the holy lands of the Bible from being desecrated by non-Christians. However, the true reason for fighting for these lands was less than holy. It was mainly a desire for economic gain that prompted the Christian leaders to send soldiers to fight in the Holy Land.
The second way one uses the word "thesis" is in reference to a major paper that one writes as a capstone for his or her bachelor's or master's degree. Whereas term papers are projects that last one term, theses are projects that last several terms. Theses are usually much, much longer than term papers, often stretching past two hundred pages. Perhaps counterintuitively, however, theses often cover much more specialized topics than term papers. For example, one may write a term paper on Herman Melville for a literature survey course, but one would be much more likely to write a thesis on homosexual symbolism in Herman Melville's Moby Dick or on some other extremely specific aspect of one of Melville's novels. In fact, one could write an entire thesis on a single paragraph of Moby Dick . The goal of a thesis is to expound fully one's opinion on a given subject and to confront and exhaust all the opposition to that opinion. Therefore, one usually specializes his or her thesis topic almost to the point of absurdity.