You know what is more frustrating than having to rip up several days worth of knitting because you got the gauge wrong?

Having to rip up several days worth of knitting because you used the wrong yarn.

I made swatches with several different yarns and then picked one combination and ordered enough for a whole cardigan. Unfortunately the alpaca yarn I left in the knitting basket was not the one I had decided to use. And I discovered this when I had knitted most of the first ball of yarn.