"Watercolor is a medium that can be as demanding and temperamental as those who choose to paint with it. But it is a colorful and exciting medium all the same – well suited to describing the many moods of the subject, as well as those of the artist wielding the brush." (Jean Burman)
Watercolor is Hard!
It can be difficult to fix mistakes. You have to really plan and think ahead. You cannot wipe off, erase, or paint over errors in the way you can with opaque mediums (oil, acrylic, gouache, etc.) There is no way back!
Watercolor can be hard to manage. You can never totally control the combination of water and pigment. Especially when it comes to washes. You can do everything "right" and still end up with a result you weren't anticipating. Bleeding, blotches, and blooms happen to the best of us.
"In watercolor, if you are not in trouble, then you're in trouble" (Selma Blackburn)
Now, you can have some control. An intimate knowledge of how your materials react, especially when it comes to how much water you're using, is a necessary skill that comes with practice.
The transparency of watercolor can be another challenge. Sketches must be light or you risk the lines being visible behind lighter areas of your work. You cannot lighten a color after it's been laid down.
There is no white paint. This goes along with having to plan and think ahead. You have to preserve your whites. If you're not a watercolor purist, go ahead and use white Gouache.. But, in my opinion, it's noticeable. I've had to train myself to not use it and instead make it a point to analyze my reference and use masking fluid/tape to preserve the whites right off the bat.
"When in doubt, leave it white" (Gene Allen)
I LOVE Watercolor.
Watercolor is so easy to clean up. I mean, it makes sense. Watercolor is water soluble. If I spill some paint on my table, I can just wipe it off. Brushes can be cleaned without chemicals/solvents. As far as I know, I can pour my paint water down the drain and it won't cause any problems...
Watercolor is portable. The pans can be dried out and kept in a tin. When you're ready to use them, add water. Paper and a watercolor tin are a lot easier to carry around than canvas and tubes of paint.
Watercolor is affordable. Because they can still be used after drying out, watercolor tubes can be stretched a lot further than other paints. I have had some tubes that have lasted 6-7 years before I'd have to buy new ones. And, I paint A LOT.
Watercolor is vibrant and luminous. Watercolors are so soft and flowy and capture luminosity, beautifully.
Watercolor can have a soothing effect. It is calming to watch the movement of paint across the paper and to watch the interaction of paint and water with paper. Painting with watercolor reduces feelings of stress and anxiety for me. Especially when it's just playing around with no expectations.
Like anything, practice makes progress. With time, the challenges start to feel less like challenges and you'll begin to (hopefully) mostly recognize the rewards. That's how it's been for me, anyway. You're learning with every mistake you make!