Sometimes, no a lot of times in watercolour, a work just does not work. An expensive watercolour sheet wasted? Not me, I have second go on the reverse side of the paper, so at least I can console myself that all is not lost. The results can be liberating, in that, one is no longer worried about ruining an expensive sheet of paper, but can relax and let go as it does not matter now, the sheet was heading for the recycle bin anyway. I currently use heavy 300lbs paper, so this is possible.
The figures below were painted on the reverse side of a failed watercolour, so it's now a keeper.