REALISTIC DRAWING is much easier than you think. 
The problem is we do not see OBJECTS properly, we do not even take time to watch them before we start  to draw them. Why is that? Because the way our brain (left hemisphere) approaches things is not suitable for drawing. It is suitable for reading, speaking, writing, mathematics, science, managing things, etc. (very useful, of course) but not good for drawing realistic pictures. 
You need to learn how to allow your right brain hemisphere to do its job. If you do so, you will draw wonderfully!