Once, a Chinese traveller came to meet Kautilya (Chanakya). It was dusk and darkness had just started to set in. When the traveller entered Chanakya's room, he saw that Chanakya was busy writing some important papers under the lighting of an oil lamp. You know that there were no bulbs or tube lights in those days, since there was no electricity. So, in those days people used to light oil lamps. Chanakya smilingly welcomed his guest and asked him to sit. He then quickly completed the work that he was doing.
But do you know what did he do on completing his writing work? He extinguished the oil lamp under which he was writing and lit another lamp. The Chinese traveller was surprised to see this. He thought that maybe this was a custom followed by Indians when a guest arrives at their home. He asked Chanakya, "Is this a custom in India, when a guest arrives at your house? I mean, extinguishing one lamp and lighting the other?" Chanakya replied, "No my dear friend. There is no such custom. Actually, when you entered, I was working. It was an official work, pertaining to my empire, my nation. The oil filled in that lamp has been bought from the money from the National treasury. Now, I am talking to you. This is a personal and friendly conversation, not related to my nation; so I cannot use that lamp now, as it will lead to wastage of the money of the national treasury. Hence, I extinguished that lamp and lit this other lamp, since the oil in this lamp has been bought from my personal money."