Honest to He Who Writes Knitting Patterns, when it comes to ribbing it should be in bright red, bold letters:
"[SIZE="5"][COLOR="Red"]YOU WILL NEED TO PAY CLOSE ATTENTION DURING THE RIBBING PROCESS. VERY CLOSE ATTENTION. ATTENTION AS YOU HAVE NEVER, EVAR PAID IN YOUR LIFE[/COLOR][/SIZE]"
No matter how long you have been knitting, you always have to A) make sure you have the correct number of stitches (especially if knitting in the round) and B) make sure you know your knits from your purls if you're flat knitting. Then you have to keep track, knit one, knit two, purl one, purl two, rinse, repeat. Ribbing is not a part of your work where you can go on auto pilot like you cant when the pattern reads "knit around for the next 9 1/2 inches".
Ribbing is not difficult, it's just incredibly tedious. You have to pay very close attention to your stitches.