When you are frustrated and thinking, "I probably just have limited ability at maths", that's just anxiety.

I'm not sure I buy this, though. If you view the ability as learning ability, or what I call elasticity over here, then it seems like I can say "I find it more difficult than I expect to learn a foreign language; I'll downgrade my expected elasticity for foreign languages" and that might switch the EV of spending more effort on learning foreign languages from positive to negative. If there are multiple things I could do, and which thing is wisest depends on the relative elasticities, then trying to estimate those elasticities seems useful and doable without hitting the hard limit.