https://hackernoon.com/debugging-smart-contracts-with-truffle-debugger-a-practical-approach-f56bf0600736

Bugs! Bugs are aliens that creep into a programmer’s code at night when no one is watching and alter the state of a working code. These aliens have only one mission — to frustrate the life of a programmer. How does a programmer kill a bug before he dies of frustration? Yeah, you got it right! By debugging and removing the buggy code. But why would a programmer go into a debugging war without the right tools? If a programmer is going to debug he better do it the right way, using the right tools.

In smart contract development, like traditional centralized software development, bugs creep into the smart contract developer’s code during the development lifecycle of the smart contract. While there are ‘Etherillion’ reasons why smart contracts could be buggy, one thing remains important, all bugs must be removed before the smart contract is deployed on the mainnet, or else, we risk losing funds and ultimately, the credibility of the smart contract.