I received an expensive, though not particularly good, education, and I think I'm reasonably intelligent, but I can't half be a bit thick sometimes.
Simple things sometimes elude me. I'll approach things in a certain way that, on reflection or being shown how, seems absurd. Anything to do with numbers or geometry completely eludes me. I can't cut a roof, and I've been hopeless with money. But I present quite well, and know a enough about a few things to be quite effective at them. But I can definitely be a bit thick.
I live in a strange part of the world, one where you need to be wary of prejudging people. I get people in my shop who look and sound like half-wits, who can hardly string two words together. I often watch them leave, and they will almost inevitably climb into a new £120,000 Range Rover or Porsche. Some of them appear variously in both, and a sports Bentley to boot. I know people who have had a terrible education who are so articulate and funny that they run circles around me. I'm certainly thicker than they are.
Liz Truss? She seems socially awkward, and presents terribly. I heard her interviewed on woman's hour recently. She didn't seem particularly inspirational, but seemed bright enough. Bright enough to be FS? Well, she should be in charge of her brief, and she clearly wasn't the other day. Starmer was mentioned. He has a pipsqueak voice, and I think presents poorly (as a politician). But he is a successful barrister, fleet of mind by definition. It's unlikely that you can become one of those if you're thick.