Japanese readings for Kanji

Hello there!! 毎度です。
I haven't been posting for a while and felt it was time to drop some lines in here.
I have some topics in mind and will be posting more regularly in addition to putting more videos on my youtube account.

Anyway, today's topic is about why is it so difficult to learn Kanji.
The main reason for that is that contrary to Chinese and Korean, where IN PRINCIPLE there's only one reading for each character (了，的，得，地，行 are some of the exceptions I can remember in Chinese), Japanese might have several readings.
The reason for that is that the Chinese characters were borrowed during 3 different periods and that resulted in the following readings:
呉音(go'on: go reading: readings brought to Japan from the 4th through 6th century)
漢音(kan-on: kan reading: readings brought to Japan starting from the 7th century)
唐音(tou-on: tou reading: readings brought to Japan during the Heian period, which started in 794 and the Meiji period, which finished in 1912).

The readings above are included in the 音読み(on-yomi: phonetical reading for the Kanjis).
In addition to the readings above, Japanese also use the kun-reading(訓読み), which is an adaptation of Japanese words to the Kanjis.
For example, the kanji 学 can be read as "manabu" in Japanese but has its on-reading as "gaku" (similar to the Korean reading of the same character).

I made the following video for youtube recently and hope it helps shedding some light on this subject:
http://www.youtube.com/watch?v=htgVK9p5zc4

Cheers!!