When I believe in something, it's like I really trust or think it's true, such as when I believe I can do well in a test because I've studied.

But when we say 'Having Belief Isn't Enough,' it means that just my belief alone isn't always sufficient or all I need. It's like saying,

Even though I believe I can do well, I still need to study hard and prepare. My belief by itself doesn't guarantee success.