As a competent home cook, what is a basic skill you can't seem to master?

I consider myself a competent home cook. I've been cooking and learning about food for over a decade. I can cook most things without a recipe, and it is very very rare that something I make isn't tasty enough to eat. Not all fine dining, mind, but good enough. Hollandaise sauce, poached eggs, steak, bread. Decent technique and skills. Not a chef, but good enough for myself and my family. etc etc. I'm only saying this for context.

But, for some reason, I can't make mashed potato.

I can make adequete mash. Slightly lumpy, or gloopy, or sloppy. I have spent hours researching the science to try and perfect my technique. I have tried probably dozens of recipes. Ricers. Pushing through a sieve. Baking the potato first. I have not yet managed to achieve perfectly smooth, fluffy, tasty mash.

Anyway, what are your cooking downfalls that you can't seem to master, no matter how competent you become in the kitchen? Share your woes and make me feel better.