Yarn Spaghetti
    I have a "rule":
    
        - If I discover a small mistake as I'm knitting, I'll let it go (Depending on where it is) 
 (Maybe I've missed a shaping instruction, I'll just catch up and ignore the mistake)
        - Mistake #2 will also get ignored (if it's not too noticeable) 
BUT . . .
        - the 3rd boo-boo gets ripped.
        - If all 3 mistakes are bad enough, I'll start all over. 
There have been lots of bowls of "yarn spaghetti" over the years (as recently as this week). 
     Mistakes happen ! Be prepared
 Getting comfortable with ripping rows is essential for machine knitters. Have you ever been knitting and missed an increase or decrease instruction? Maybe a knot or a yarn slub slipped thru and is showing a few rows back. Time to rip ! But don't lose track of your row count.