What are some of the innocuous looking moves that each of you personally finds very difficult?

For me it's *walkdowns-updowns* (oh my gosh) and *side hip raises* (I seriously don't even know what I am doing, and why my elbows are hurting so much).

I would welcome any guidance on how to make these easier. Feel free to post your own bugbears in the comments so others can pitch in and advise if possible!