Or even worse…drop a stitch and not notice until 20 rows later. It is very dangerous to crochet, and more so knit, when one is tired or weary. Mistakes happen and some of them can be very nasty to try and fix.
When one is crocheting/knitting, one should be seated comfortably, bright-eyed and bushy-tailed. :D Attentiveness is the key to excellent crocheting/knitting. My teacher told me to admire my work after every row or two; this is a good way to catch those nasty mistakes before getting too far.
When one is knitting lace, the best life saver is a life line (a piece of yarn/thread, lighter in weight then what you are working, strung through your stitches at the beginning of a lace pattern. This aides in case you have to frog your project due to an error. You only have to frog back to the life line!
Bottom Line: A hooker should be attentive to his/her crafting.