There are many exceptions to the rule
On the whole. however, most people have a substantial degree of understanding.
Given an idea, they can extend it and apply it.
Indeed, this seems to be the basis of the thinking process.
On the other hand, there are people who do not seem able to develop an idea at all, and this occurs at both ends of the thinking process–from a lack of capacity or from too much brilliance.
That is, some individuals get flashes of brilliant insight but are unable to do anything with them (even so-called creative people can be so handicapped).
And some people can only develop or add to given ideas.
–Rabbi Adin Steinsaltz