Oh, my! What a question! I am humbled by triangles and anything bias. Curved seams. Getting things to measure what they are supposed to measure. Need I go on? And to complicate matters, when I get to "simple" sewing as in a mug rug with a purchased insert..to get the corners to be corners and not look so 'homemade.' Some days just make me wonder why I am so intent on mastering all of this! I used to sew better when I was in my teens...and I know way more now....and have more experience! Go figure!