Originally Posted by Northumbrian

You vote out the party in government, because after several years they're doing a bad job.
You vote out the new party in government, because after several years they're doing a bad job.
You vote back in the first party mentioned, because you hope they'll put right the mistakes of the last government, and hope the first party have learned from their previous mistakes (if you can remember that far back).

Then repeat the process again. Unless you want to vote for a minor party or not at all.