5 things I can´t do, even if I try really hard. And in my opinion, efficiency is about knowing your limits and not wasting any time getting better in this weak areas.

Tying shoes. There is a childish way and a sophisticated knot. I can only do the first and then add a double one for security.
Baking. I tried three times in the last week and failed. The “carrot cakes” had to go straight into the bin. Not edible.
Navigation. I don´t have any sense of orientation. So, don´t count on me finding the way – especially driving to a new location.
Climbing. It doesn´t matter if this means going up a ladder or climbing a rock. I can´t stand situations, where I might fall.
Remembering numbers. There is just no space in my brain for numbers of any kind. Nether in short, nor in long term memory.