Today I was out painting on the marshes, and the reflections and patterns were unbelievable as the tide flowed serenely in. Working in watercolours, plein air, not from photographs, one can become schizophrenic as things change so quickly. Added to that changeability of light and pattern, you have a lot of humidity, so watercolours seem to take for ever to dry. So I was doing what I seldom do, doing two paintings concurrently.
Pretty soon, I remembered, a little wryly, a remark I found that Hans Holbein the Younger had made: "everything began with a drawing..." How true! If I had not made a relatively loose but nonetheless careful drawing before I started each painting, I would have been in deep trouble. In one painting, I got fascinated with the reflections of three docks along a creek edge, and the play of light on their pilings, roofs, etc. However, between the drawing and later (sort of!) completion of the watercolour, people had moved boats around, the tide had come in, the sun had gone over and clouds had come up. Without at least a rough "road map" underneath, I would not have known how to continue the painting at some points.
I think I first learned to the value of an initial under-drawing for a watercolour many, many years ago in Alaska. I was doing a landscape of the dramatic mountains and inlets near Homer, and to my delight, there was a little red plane parked at just the right focal point. I had drawn it very roughly, intending to return in more detail as I got more to painting that part... Painting away happily, I suddenly realised that I was hearing the sound of a plane engine starting up. Before I could remedy my omissions of detail, the little red plane had sailed up into the air and disappeared! So much for my focal point!
In other words, draw, draw and draw again - one never regrets it.