Why did Imran sort the buttons a second time?

On his first day as an apprentice in the tailoring shop, Imran expected to sew. Instead, Ustad Karim gave him a box of buttons and told him to sort them.

On the second day, he sorted thread. On the third day, he swept the floor, and on the fourth he sorted the buttons again, because a customer's child had knocked the box over.

By the end of the second week, Imran was angry. "When will I learn to sew?" he asked.

The old tailor did not look up from his machine. "Tell me," he said, "how many kinds of white thread do we have?"

"Four," said Imran at once. "Cotton, silk, the thick one for buttons, and the cheap one for tacking."

"And where are the small pearl buttons?"

"Third drawer, left side, behind the brass ones."

Ustad Karim stopped the machine. "A tailor who does not know his own shop," he said, "spends half his day looking for things. You have learnt the shop. Tomorrow, you will learn to use the measuring tape."

On the next day, Imran measured his first customer. His hands shook a little, but he knew exactly where everything was, and when the old man asked for chalk, he had it ready before the sentence was finished.