It's by giving voters the opportunity to put their favourite candidates, whoever they might be—even someone who has little chance of winning—first on their ballots. Under the current system, if I vote for an unpopular candidate, a candidate who is unlikely to win the seat, I'm in effect throwing away my vote. My voice in favour of that candidate isn't being heard, and so I have a strong incentive to vote for someone else who does have a chance of winning.
Under majority rule or alternative voting, we can see from how people have voted which parties are truly favoured.