Here's one really simplistic way of describing government. The government makes laws, people have to follow them. Now, we can sort different types of governments by answering the question, "Who makes the laws?"
In a dictatorship, you have one person making the laws. In a pure democracy, every member of the state has a say in making the laws. Dictatorships can be quite efficient. One guy makes the laws, no one else gets a say. If the dictator wanted to make a law that Friday would be no pants day, then bam, it's done. No need to wait for anything to make the law official. Democracies, on the hand, are quite inefficient. Sometimes it takes a while to get consensus on a potential law. Lots of candidate laws never see the light of day. If there were an omniscient, morally perfect leader, then a dictatorship would be the best form of government. Unfortunately, no such individual exists. So, democracy, inefficient as it is, works out better than a dictatorship, since it allows people to decide for themselves what is best for them. Dictators can and do often act in a way that benefits themselves at the expense of the other members of the state.
Another reason to think that dictatorships are no good as a form of government is that it is possible to manipulate the dictator to make laws that may not be beneficial to everyone. Let's say you and your family were members of a dictator state. If you wanted a law that made it easy for your family to get high-paying jobs, then you'd have to go through dictator, since the dictator makes all of the laws alone. You could get the dictator to make such a law via some form of manipulation, e.g. bribery, blackmail, false information, etc. A dictator who is corruptible, ignorant, or unreasonable would be susceptible to various forms of manipulation, and could thus instate laws that are harmful to the majority of citizens.
We would thus think that democracy is better because it's harder to manipulate a bunch of people than it is to manipulate one person. All things held equal, this is true. Even though it may be relatively harder to manipulate a bunch of people, it is still certainly possible to do such manipulating with all of the mass media technology that we possess currently.
That's one reason to think that pure democracy is an inferior form of government to what I call democratic epistocracy. An epistocracy is a state run by those who meet some minimal standard of rational aptitude and being informed. John Stuart Mill championed a form of epistocracy where the number of votes you had varied positively with the degree to which you were informed and the degree to which you were capable of reasoning. This is democratic epistocracy in a nutshell. All citizens get a vote, but those in the know and are capable of thinking things through get more votes.
I think that democratic epistocracy is less susceptible to manipulation than pure democracy. Like pure democracy, you have to deal with the prospect of trying to manipulate a group of people rather than one person. Unlike pure democracy, those with the most say in what laws get enacted are less likely to manipulated via misinformation, appeals to sentiment, and bad reasoning. Of course, such individuals are not incorruptible, but at least they are not easily led astray by soundbites and such. This added resistance to manipulation is one reason to favor democratic epistocracy over pure democracy.