Watercolour is hard due to its unpredictable nature. Watery pigment flows wherever it wants, which makes it difficult to control. And since watercolour is translucent and appears lighter once the pigment has dried, it's hard to fix mistakes because they show through the layers.You need to know what you are doing because you can't make changes by painting over them. You also need to be careful that you don't damage the surface you are using by repeatedly wetting it.