McCain can win Republicans
The independents who fueled John McCain's previous victories couldn't vote in Florida, so McCain pulled together enough moderate and liberal Republicans to overcome Mitt Romney's advantage with conservatives. McCain fared especially well with Cuban-Americans and Republicans dissatisfied with the Bush administration.
Voters like winners
Rudy Giuliani's strategy was to accept early losses in smaller states so he could dominate Florida and show national electability. But voters didn't share his comfort with those losses. Giuliani's anemic results leading up to Florida undercut the core point of his campaign.
You can't win if you can't campaign
In Iowa, the turning point for Barack Obama was his rousing speech to a Democratic dinner and the TV ads it spawned. But Obama couldn't give the speech in Florida because of a September pledge not to campaign. That froze the race at September levels, when Hillary Clinton had a commanding lead.