It's just a part of our first past the post system. Even though a candidate wins the election, he or she may not receive the majority of the popular vote.
Let's say that a candidate wins the election against the other three candidates.
Candidate #1 receives 26% of popular vote
Candidate #2 receives 25%
Candidate #3 receives 25%
Candidate #4 receives 24%
Even though candidate #1 receives only 26% of the popular vote, candidate #1 wins the election because the other three had less.
If this happens in the other 307 ridings in Canada, where candidate #1 wins only 26% of the popular vote, every candidate #1 would win and the entire House of Commons would consist of candidate #1's.
Of course this is really rare in Canada because the conservatives and the liberals are the only two super parties in Canada. These two usually win the most often. The New Democratic Party gets votes, but only enough to win a few seats, and the Green Party hardly ever wins. The Bloc doesn't count because they only represent Quebec.