What is the Idea behind the 'Too Big to Fail' saying?

-The Bailout for Banks had been a Large Need for the Banking Industry, as their Size was too Big for the Economy. -If a Large Bank had Collapsed, the Panic and Fear would lead to an overall Meltdown in the Financial System -The UK, USA and Europe had to deploy Large Bailout Schemes in 2008, even if it costed Billions of $$$$$