But a higher level of intelligence means a person can accomplish a given task with less effort than someone with lesser intelligence. If both people have the same level of innate "drive", the person with more intelligence is more likely to simply accomplish the task, as it takes less effort for them. The less intelligent person might not, because to make up for his lack of intelligence, he would need to put in more effort than his level of motivation allows.
First assertion is correct. A person with a higher level intelligence can accomplish a mental task faster and with less effort. But part of that is because of practice that goes along with it.
When I was in high school and college, it didn't take me very much effort at all to do anything academically speaking. Even now, it doesn't take me as much effort as many others, but because I am also out of practice, it would still take me longer than someone who wasn't.
Take calculus for example. Back in the day I had zero problems with calculus or really any math. Part of the reason I'm a good programmer. But ask me about formulas today and I couldn't give you a calculus problem or formula off the top of my head. The memory just isn't there. It would take me longer because I would have to rebuild my memory back partly, and rebuild my though process sequence. No different than someone that hasn't ridden a bike in a LONG time. They know they once did it, they remember generally how to do it, but once they try again they would have to rebuild muscles, muscle memory, and other reflexes that would have possibly disappeared over the years.
There are just something that practice makes autonomic when it comes to everything. Both the physical world and the mental world.
However, most people have a limit to various things. I do. I am crap at music for some reason. I really am just about tone deaf when it comes to singing and picking out exact notes with my ears. Doesn't mean I don't appreciate good music, it just means I have a severe limit imposed on my ability to make music. I also know I'll never be a football star, basketball star, or underwear model. Intellectually speaking for myself, I never knew or reached my limit. I just decided to focus on something I found myself enjoying, computer programming, and stuck with that.