same with お楽しみに~~♡ , or お大事に~
We can illustrate this with an English example. Basically finish the sentence:
Where are my Lucky ________?!
Dude, what the ______?
“Hasta la vista _______”
As you can see you just know what goes there and as it relates to Japanese, its just shorter. Think about all the times that a Japanese person would ALWAYS have to finish their sentence. Mad awkward.
Also here’s another example:
[3/8/2011 12:20:11 AM] missingno15: で、toshさんは外国を勉強してるの?
[3/8/2011 12:20:13 AM] missingno15: 英語?
[3/8/2011 12:20:39 AM] tosh: 英語だよー。
[3/8/2011 12:20:53 AM] tosh: 英語がふつうにはなせるようになりたい!
[3/8/2011 12:21:00 AM] tosh: アメリカにも旅行にいきたいし。
[3/8/2011 12:21:53 AM] missingno15: そのために英語を?国際旅行?
[3/8/2011 12:22:27 AM] tosh: そうだよ!アメリカのドラマ、映画、大好きだしね
[3/8/2011 12:22:35 AM] missingno15: いいな
So in short, I would kinda think of it as just like “finish the sentence”.
But what do I know, I’m just a beginner ヽ(´ー`)ノ