みっか みつき さんねん
mikka mitsuki sannen
(This can be alternatively written/pronounced as:
みっか みかげつ さんねん
mikka mikagetsu sannen
Three is an important number in the Japanese collective consciousness. Oh you'll hear a lot about numbers like 4 and 9 as harbingers of suffering and death, or 8s representing bounty... but 3s are where it's at in terms of demonstrating resolve.
What do I mean by this? Let's take a look at some Japanese expressions and Japanese cultural practices that all involve threes.
Three is the magic number for gift giving at weddings: 30000円 is the traditional amount for a present, and if you choose to give gifts like dinner ware, or bath towels, or anything domestic, you should always give them in groups of odd numbers, like 3 or 5, with 3 being the standard. While I imagine that in the states, couples gifts in groups of 2, or even family starter gifts in groups of 4. In Japan, however, the idea is that even numbers can be evenly divided and are not appropriate for weddings, which should be about lasting bonds. A group of three (man, woman, and child perhaps?) can not part ways so easily.
And there's another marriage tradition with threes that I learned about recently. It's common, still today, for a suitor to be turned down by the bride's father three times before receiving consent.
This ties in with the general idea that Japanese people will say "No" thrice before accepting things. When you offer to pay for a meal, (or even just for your portion of a meal) Japanese people will often refuse. If you do want to pay, try offering more than four times. They might just be being polite.
On the same theme of persistence, remember 三日坊主? Three days is the make or break point. Someone who's sticking with it after three days is probably not going to give up.
So take the 三日 from 三日坊主, as the period required to see what a trade, hobby, or regular practice requires, and we can start to work on the meaning of today's phrase.
Watch for three days, learn for three months, practice for three years.
Sorry for the lack of a definition in Japanese, but definitions seem to vary. A man who gave me a lift through Shimane-ken explained that this was the way that you become an expert at something, the way you make it your own.
Some sources on the web equate this expression to the ことわざ 「石の上にも三年」, which involves enduring boredom and suffering to achieve greater results. Notice how that takes three years too?
Do you know any other Japanese expressions or customs involving threes?