A Farmer – let’s call him "Farmer Andy from Germany" is concerned about his prize cow, Julia. He is worried – the good times may be over.
He is so concerned that when his dairyman tells him that Julia is in the field, happily grazing, he says he needs to know for certain. He doesn't want just to have a 99 per cent idea that Julia is safe, he wants to be able to say that he knows Julia is okay.
Farmer Andy goes out to the field and standing by the gate sees in the distance, behind some trees, a white and black shape that he recognises as his favourite cow. He goes back to the dairy and tells his friend that he knows Julia is in the field.

At this point, does Farmer Andy really know it?

The dairyman says he will check too, and goes to the field. There he finds Julia, having a nap in a hollow, behind a bush, well out of sight of the gate. He also spots a large piece of black and white paper that has got caught in a tree.
Julia is in the field, as Farmer Andy thought.

But was he right to say that he knew she was?

In this case the farmer believed the cow was safe. He had an evidence that this was so (his belief was justified) and it was true that his cow was safe.

However, we might still feel that the farmer did not really know it; his justified true belief was actually operating independent of the truth. Herein lies the core of the problem of 'knowledge as justified true belief'.