The simple absence of data has never been enough to stop fools from inventing theories. 

It is said that coming to conlusions without first analysing the facts is dangerous. But fools over the history of human civilization, have made this error of inventing theories without having enough data to prove them. We have always made theories by extra-polating our data or going ahead with theories without any reasonable data backing them. For instance, without going out of earth and exploring the night skies, people theorize earth to be as the center of the universe. Some even provided the theory of earth being flat without ever looking at the earth from outside or conducting experiments to prove otherwise.

Thankfully, in today's science, almost every theory is based on the analysis of extensive sets of data. According to the scientific process, a person has to first come up with a hypothesis. Afterwards, in order to prove the hypothesis, he conducts certain experiments and carefully record the observations into data sets. These data sets are then analyzed to either disprove or prove the hypothesis. If it is proven successfully, then only it becomes a theory. Almost, all of the formal areas of study these days, follow the same scientific principle as described above. Infact, in today's world there is an over-abundance of data. For instance, if somebody wants to study the weather, today's weather sensors will provide thousands of data-set points every second about various conditions of weather. Previously, however, without computers and sophisticated sensors, data was recorded only twice or thrice a day. Thus, with the introduction of computers, scientists have got a means of analysing huge amounts of data-sets to increase the accuracy of their findings. Also with internet, and various visualization tools, data is increasingly being used by every scientist to give a theory.

But not everybody follows the scientific process towards making theories. Theories are still being made without data and circulated from one person to another. These theories which are often superstitions or beliefs of one fool spread to form urban myths and legends. There is a even popular Discovery channel show: MythBusters which tries to bust as many of these urban myths as possible. Some of these myths can be very believable while other can be really outlandish. To give an example of an outlandish theory, some people believe that if they are going on a street and a black cat crosses the path in front of them, if they go ahead on the same path, something bad will happen with them.

However, most of these theories also have a good justification behind them. But without data, they can quite often be wrong. For instance, many people believe that by eating sugar, children become over-active and go out-of-control. The reasoning behind the theory is that sugar contains carbohydrates which provide energy and this over-abundance of energy causes children to become hyper-active. Since, there was no supporting data, the theory was never tested. But we now know, that this is a myth since although sugar has energy but extracting energy from it requires digestion and often with extra sugar a child may feel drowsy.

Although people will keep on making new theories, some scientific, some foolish, it is upto us to choose what to believe in. If you are a rational person who believes in science and the importance of data, then you will refrain from believing in the theories purported by fools. But, the simple absence of data will never be enough to stop fools from inventing theories.