The heron painting was the turning point. I'd done the bird itself fine — three careful sessions, built up in layers, happy with the feather texture. Then I got to the water underneath and spent two frustrating afternoons making it look like...water in a colouring book. Even, controlled, dead.
The problem was the brush. A brush blends. It softens. It smooths things out. Which is exactly what you don't want when you're trying to paint a reflective surface with movement in it. Real water has hard edges where a ripple catches light, then nothing, then another edge. It's inconsistent. The brush was averaging everything out.
I picked up a palette knife mostly out of frustration — scooped up a pile of mixed blue-grey and scraped it across the bottom half of the canvas. Stood back. That was it. That's what water looks like. Loaded, uneven, with bits of underpainting showing through where the knife hadn't quite caught the texture.
Since then I've used knives almost exclusively for any kind of reflective or moving surface. The loss of control is the point. You can't micromanage a knife the way you can a brush, and for this kind of subject that's exactly what you need.
Worth experimenting with if you've been fighting a painting and can't figure out why it feels flat.