I think one image can explain why best:
This is the famous incident. During the 2006 election, we saw the Christmas Holidays take place right in the middle of the election. Before the holiday, the polls were so stable, comedians were cracking jokes. After the holidays? The Tories were clearly in the lead and marched on to victory.
A quick look at Alberta shows that the April 6th Easter holiday also produced a change, as that's when the NDP's march to victory began.
Even Ontario had a small change, over the may24, with the Liberals solidifying.
There are logical reasons for this as well. As anyone who has ever had a family gathering will know. Anything can come up at the table.
This is not to say that families all across Canada are sitting down to their Turkey and discussing the merits of Stephen Harper's electoral strategy against Justin Trudeau, but rather, they share feelings.
All it takes is for Uncle Bob to say "And don't get me started on that Harper" or for Auntie Jane to add "I hope that Trudeau wins". At that moment, everyone at the table has an opinion, but they may not share it, but you can see it - in their eyes, in their body language.
People who are on the fence will be scanning the table, and if they see "hey, all these guys think the way I do, maybe I'm not so crazy" they will be much more liable to change their mind, or pick a choice.
In 2006, people said "Harper's not so scary". In Alberta they said the same thing about Notley.
What will be the question this time?
Nobody can know for sure, but my guess is two fold.
1 - "Harper has done a poor job."
2 - "Trudeau simply is not ready."
People will have opinions either for or against these two statements. If both statements come out "yes" the NDP could see a rebound. If both come out "no" the Tories could win a majority, same as if even the first comes out "no."
However, my 'gut' tells me the answer to the first is "yes" but the answer to the second is "no". If my gut is right about this, people, in a day or two, sit down with family, and realize... you know what? I am comfortable with the idea of Prime Minister Justin Trudeau.
And Majorities have been built on less.