What lesson was Shammai teaching by lighting one less candle each night?

The Talmud offers two answers to this question. Here is another possible way of understanding Shammai’s reasoning. When the Torah describes the menorah the following details are conveyed:

דַּבֵּר֙ אֶֽל־אַהֲרֹ֔ן וְאָמַרְתָּ֖ אֵלָ֑יו בְּהַעֲלֹֽתְךָ֙ אֶת־הַנֵּרֹ֔ת אֶל־מוּל֙ פְּנֵ֣י הַמְּנוֹרָ֔ה יָאִ֖ירוּ שִׁבְעַ֥ת הַנֵּרֽוֹת׃

(במדבר ח:ב)

Speak to Aharon and say to him, “When you light the lamps, let the seven lamps give light towards to center of menorah.” (Numbers 8:2)

Rashi explains that the way to perceive the menorah is to picture all the different lights turned towards the middle. Perhaps Beit Shammai is suggesting that our celebration should resemble the Menorah of the Beit HaMikdash: A single flame is to be the focus, representing the Oneness of God.