I've come to this same question over & over again, also due to same reason. So let me answer this by saying what wrong I was doing. Might be helpful for someone.
I was creating component via angular-cli
by command
ng g c components/something/something
What it did, was created the component as I wanted.
Also, While creating the component, it added the component in the App Module's declarations array.
If this is the case, please remove it. And Voila! It might work.