I am struggling to understand why Volatile fields exist in C#.

The documentation states that they ensure the required order of
processing.. the example given by Microsoft is :

using System;
using System.Threading;
class Test
{
  public static int result;  
  public static volatile bool finished;
  static void Thread2() {
     result = 143;    
     finished = true;
  }
  static void Main() {
     finished = false;
     // Run Thread2() in a new thread
     new Thread(new ThreadStart(Thread2)).Start();
     // Wait for Thread2 to signal that it has a result by setting
     // finished to true.
     for (;;) {
        if (finished) {
           Console.WriteLine("result = {0}", result);
           return;
        }
     }
  }
}
produces the output:

result = 143
In this example, the method Main starts a new thread running the
method Thread2. This method stores a value into a non-volatile field
called result, then stores true in the volatile field finished. The
main thread waits for the field finished to be set to true, then reads
the field result. Since finished has been declared volatile, the main
thread must read the value 143 from the field result. If the field
finished had not been declared volatile, then it would be permissible
for the store to result to be visible to the main thread after the
store to finished, and hence for the main thread to read the value 0
from the field result. Declaring finished as a volatile field prevents
any such inconsistency.

why on earth would the runtime or hardware or operating system change
the execution order??  surely if you put the 'result' assignment
before the 'finished' assignment, you would expect the execution of
them in that order??? I am confused?  Are microsoft saying that we
cannot trust the execution order when dealing with threaded execution?

Brianos