However, there are some people who will never never never go solo. And some have gone solo who should have been advised to take up golf.
I have had in a long career five students, two women, three men, who seem to be missing a circuit in the brain. After struggling with a father and son, aged 40 and 20 respectively, who seemed to be deteriorating over a weeks course, I asked the highly experienced Chief Flying Instructor to fly with them. I was beginning to think it was my instructing at fault! CFI told me that these two individuals would/should never go solo, and it was possibly hereditary!
Another chap did go solo, and frightened us on a regular basis, and was finally asked to give it up. And the two women displayed serious lack of concentration. On the ground as well as in the air. Dear me.