In 2 Kings 13: 18-19, Elisha told the king of Israel to strike the arrows to the ground. The Bible doesn't say how many arrows were there. But we can guess that it was a handful of arrows or a quiver full of arrows, so that the king could take a bunch of them in his hand.
Elisha's exact command to the king was this:
"Then he said, 'Take the arrows,' and he took them. And he said to the king of Israel, 'Strike the ground,' and he struck it three times and stopped." (2 Kings 13:18)
So the king took the bunch of arrows and struck them altogether against the ground three times.
We can see that Elisha didn't say stop or how many times to strike the ground. However, in Elisha's previous command, Elisha had told the king to shoot an arrow.
"He said, 'Open the window toward the east,' and he opened it. Then Elisha said, 'Shoot!' And he shot." (2 Kings 13:17)
One can assume that the king of Israel tried to shoot the arrow as best he could and as far as he could. We can assume this because no king wants to be a bad shot.
However, when the king of Israel struck the arrows to the ground, he didn't do his best. That was why Elisha got angry. The king probably thought striking arrows against the ground was a little foolish. So he did it three times and stopped. But he should have done his best and kept striking the ground until Elisha said stop.
Then he would have at least struck the ground 5 or 6 times and maybe even more.
"So the man of God was angry with him and said, 'You should have struck five or six times, then you would have struck Aram until you would have destroyed it. But now you shall strike Aram only three times.'" (2 Kings 13:19)
It is a lesson to trust God and be diligent to do one's best. Sadly for the king, he didn't do his best in regards to striking the arrows to the ground.