Mental illness...I chose "the human mind," but I didn't choose it so that we could fix stupidity, whatever that means. I would like the next 150 years to see the kind of progress in mental health that we've made in physical health over the last 150 years.
If you've ever known someone with a mental illness, maybe something as simple as OCD, you'd know how life affecting it can be. There are millions of people out there who have their own goals and ambitions, but they're wasting much of their lives just trying to cope with their illness and get through the day. It doesn't help that a large percentage of the population doesn't really believe that mental illness exists. The responses I've heard are often like telling a deaf person that they'll just have to try to hear harder. I feel like we're still in the pre-germ stage of medicine when it comes to mental illness. Diagnosis is imprecise. Response to medication is highly variable, and with an uncertain diagnosis, patients can waste years trying different variants and dosages.
Another problem is that people think of the body as a shell with a magical thing inside that is you. They have a hard time thinking of the brain as a complex organ that can malfunction or be damaged in many ways. Those problems can have a profound effect on perception, alertness, attention, mood stability, etc.