I look at amazing watercolours every day and marvel at them. Every time I'm struck by the simple idea that is at the core of each one and ask myself why I can't achieve similar results. Painting in watercolour is often a disappointment when we compare our drab results with the vibrancy of some watercolour "master". if we are painting something solid, like architecture, we long to make it in clay instead or at least with the material reinforcement of acrylic or oil. Whereas oil might allow you to rework a particular effect until you get it to your liking, watercolour has an earlier cut off point.
The reason I love watercolour (and still find it infuriating) is that you cant mess it about! You can work it much more than people think (with decent paper); adding washes, taking off, drybrush, a bit of scraping maybe. What you can't do however is fudge it with more layers of paint. The decisions you make will have an impact, and so it is worth spending time thinking what that loaded paintbrush is going to achieve on the paper.
If we are to come to grips with inherent truths about painting, that it is about illusions of depth, distance, contrast and relationship, we will encounter them quickest with watercolour. Watercolours that seem brilliantly effortless sometimes are because the painter has gone straight to the point and sold us a simple illusion, and once we have accepted that basic starting point we will appreciate other things in the painting too.
For me, grappling with the ideas that make painting an illusion are the key to progress and I love the surprises that go against my logical thought. The fact that watercolour forces me to change my decision making and throw out misconceptions about how to build a visual language is enough reason to appreciate it and respect it for its honesty.