The Key To Good Component Design Is Selfishness

When developing a new feature, what determines whether an existing component will work or not? And when a component doesn’t work, what exactly does that mean?
Does the component functionally not do what it’s expected to do, like a tab system that doesn’t switch to the correct panel? Or is it too rigid to support the designed content, such as a button with an icon after the content instead of before it? Or perhaps it’s too pre-defined and structured to support a slight var