"He just needs to concentrate on it a little more."

He needed to concentrate on one wizard at a time.

Such a person needs to concentrate on 'getting their act together'.

But he needed to concentrate on the race until then.

Right now she needed to concentrate on getting to know the rest of the crew.

We just need to concentrate and not put too much emphasis on it.

But he needed to concentrate on the problem before him.

Having my own danger to face, I needed to concentrate on the here and now.

This is the field where we need to concentrate our action a little more.

This was going to be a difficult piece of work, and she needed to concentrate on it.