In FPTP, parties can win a majority government, and exercise absolute power, without actually getting a majority of votes. It ignores the fact that most voters voted for someone else! But this means that governments often make decisions that don’t reflect the majority of voters. When the next government comes in they spend half their time undoing what the last government did. Under proportional representation a government will always be made up of parties supported by a majority of voters. Any decisions they make will stick around, because they were made with the support of a majority.