Is knitting really supposed to make you cry?

I started the shawl again, and once again I had to frog. I cast on the right number of stitches. But then I forgot to do the k3 selvedge edge stitches so I didn’t have the right number of stitches left over at the end. I ripped it out and started again. I cast on the right number of stitches, double and triple checking with stitch markers. As far as I could tell I could tell I did all the stitches right, I remembered the selvedge edge stitches, and yet again I didn’t have enough stitches at the end.

What the hell?  How can I be so completely inept at what looks to be a simple pattern with only a 10 stitch repeat?  I’ve done socks, blankets, hats, other scarves, and dishclothes with more complicated charted patterns. What it the problem with this one?