I took the wrong article and changed the meaning. Is it wrong?

Question

If I say ‘’Those are the pencils which I use to write in English’’ you know that I only use these pencils so the definite article excludes the existence of other things in this category.

If I say ‘’Those are pencils which I use to write in English’’ you know that I use many different pencils to write in English, not only those.

If we follow this logic, then if I say ‘’My neighbor has the ability to repair cars’’ then it means that he has just one ability because the use of THE restricts and limits the possible variants to just one.

But it’s literally impossible to find someone who has only one ability. We all can breathe and most of us can write or whatever. Please, guys, explain what's wrong with my brain. I try to figure this stuff out like half a year but I just don’t get it. I can’t find the right patterns. Every book says that the use of the is appropriate when there is only one entity satisfying the description. Then gives easy examples like ''Could you do something about the hum?''

Answer 1

Just because ‘’Those are the pencils which I use to write in English’’ doesn't mean that you don't also draw with them as well as write in Esperanto. There is no restriction on the use of the pencils; there is of which pencils you use for one purpose. There is also no restriction on how many other pencils you might (or might not) have.

‘’My neighbor has the ability to repair cars’’

Again there is no restriction on what other abilities he has (or doesn't), or how he uses the ability to repair cars. His car-repairing skills might help him to repair a motorised lawn motor, for example. Just because he has the ability to repair cars doesn't mean he can't, for instance write English, Esperanto, and draw as well.

To add a restriction to his possible abilities you'd have to say something like 'My neighbour has only the ability to X' or 'My neighbour's only ability is Y'.