The matter wave theory question?

For the last few years Ive tried my best to understand why I cant pinpoint a particles position and momentum at the same time. Im not a student, just someone who likes to learn.

Today I came upon a Pittsburgh University site that, I believe, put it together for me.

Here goes: a sine wave is uniform and has a definite momentum. The wave represents a particle spread throughout space.

When we add multiple waves together, the result is one wave that is no longer uniform, it tends to be concentraded in one spot. That concentration represents the particles position. But since we dont have a uniform wave, we no longer know the momentum.

Do I understand this correctly? Could you add anything else?