From what I've researched (and thought a lot about), anticipation is always more powerful than the event itself. Therefore when anticipating a fun event (like a trip or a birthday) is always much more exciting than the thing itself. Likewise, when dreading a boring or tiring event (like Monday mornings or exams), you'll find yourself so much more anxious than when the real thing is going on.
And since the 'time of anticipation' has no limits (you can start anticipating or dreading something days, weeks or months before - which could lead to depression if you know you have to go through something you don't exactly look forward to at the end of the year, then spend months worrying about), I guess it's safe to say that if you can help it, choose not to be aware of things that aren't happy. Well at least until the last possible moment when you need to come face to face with it.
Of course you'll say that it's good to know earlier so that you can be prepared for it, but why choose that when you can be happily ignorant?