I think the hardest lesson for a beginning knitter is ripping out. I know there have been times when I have had to put aside a sweater or afghan I was working on because I was going to have to rip it out, maybe not all the way but enough that I couldn't face it at that time. Fortunately for me and my sanity, I always have several items on needles or something else ready to start. I think the time I had to rip out a man's cardigan sweater was the worst. It had an elaborate pattern and as I was ready to sew the pieces together, I realized I had made the back 2 inches longer than the fronts. Since it was a gift, I couldn't shunt it to the back of my closet for a couple of months but had to rip out the fronts and redo them immediately. I never made that sweater again.

One of my students refused to rip out and cast on over when she ran out of yarn, instead she joined a second ball and continued. Fortunately, the yarn was knobby and the knot was hidden in the pattern. However the next time she cast on she pulled out plenty of yarn.