The usage of "could" implies but does not require an actual attempt to be made.

I could not find him (because I never looked).

 

I could not climb the ladder (because I am missing all four of my limbs).

 

I could not dance to the music (because I am deaf).

If you "could not" do something, it simply means that something caused you to fail in the task. Not trying is (almost) guaranteed to make you fail your task.

(I say 'almost' because it is very possible to not go looking for something but end up stumbling over it anyway! Sometimes even literally.)

The usage of "could" implies but does not require an actual attempt to be made.

I could not find him (because I never looked).

I could not climb the ladder (because I am missing all four of my limbs).

I could not dance to the music (because I am deaf).

If you "could not" do something, it simply means that something caused you to fail in the task. Not trying is (almost) guaranteed to make you fail your task.

(I say 'almost' because it is very possible to not go looking for something but end up stumbling over it anyway! Sometimes even literally.)