Before I address your question, I am going to address the philosophy thats required to contain the answer I WONT give you. The philosophy will answer you direct question.
Your question was why is there a min/hr/daily fluctuation in the market? What causes these fluctuations.
Ever stood at a seashore? Ever noticed the pattern/timing/flow of waves? What are the individual causes behind inidividual waves? I am sure there are individual causes for every single wave formed. Thats too much information. So what we do is take a bigger snapshot, say hourly or 12hr snapshop and water pressure. When you map that data on a daily basis, you may/maynot see patterns. But when you scale it weekly, monthly and yearly, you will be able to identify monsoon seasons, and subtle hints of full-moon dates.
In complex systems, the relationship b/w inputs and outputs in not 1-to-1, its Many-to-Many where variable cannot be isolated. Let me give you 1 more example. Suppose a bridge was built 50 years ago. Every day 18wheelers use the bridge but 1 day a small car goes over the bridge and the bridge falls. Are you going to blame the car? Did the car make the bridge fall? No, it simply added to strain buildup over the years.
Now to capital markets. Look at GOLD. Its a 5 year chart going from $700 to $1800+. Forget all the "news", developments and conspiracies about Gold and just look at the trend. What does the trend tell you till May 4th 2012? Its going up. And as soon as you break the trend, you start winding down your positions and start building short positions.
In Complex systems, Correlation are signals and causation is noise. More than technical jargon, complex math, smart sounding bull$**** words and british accent, its the philosophical approach that helps you organize observations of reality and help make sense of it.