After nearly twenty years of teaching, I have noticed what has most discouraged some students from pursuing the study of watercolor. In a nutshell, it is the lack of understanding of how the pigment reacts to water.
When a beginner attempts to mix a pigment with water and then begins to paint, the pigment is either too saturated with water and appears much lighter than expected. By adding more pigment and water to make it darker, a mess occurs. This, in my opinion, is what discourages or frustrates the beginner more than anything else. I know, because I have suffered through this when I started painting in watercolor.
Eventually, through many attempts at painting, you will learn from past mistakes. To save you the aggravation, I would recommend taking a scrap piece of watercolor paper and experiment with putting pigment on a wet surface, a dry surface, a damp surface, and both a wet and dry surface and watch what happens when you paint a single stroke over these various surfaces. Practice this with different pigments until you become familiar with how the pigment reacts to the water to pigment ratio.