Вот что сказано в документации на этот счет, документация в оригинале, надеюсь что вам не составит большого труда понять:
Error handling: Assert, Require, Revert and Exceptions
Solidity uses state-reverting exceptions to handle errors. Such an exception will undo all changes made to the state in the current call (and all its sub-calls) and also flag an error to the caller. The convenience functions assert and require can be used to check for conditions and throw an exception if the condition is not met. The assert function should only be used to test for internal errors, and to check invariants. The require function should be used to ensure valid conditions, such as inputs, or contract state variables are met, or to validate return values from calls to external contracts. If used properly, analysis tools can evaluate your contract to identify the conditions and function calls which will reach a failing assert. Properly functioning code should never reach a failing assert statement; if this happens there is a bug in your contract which you should fix.
There are two other ways to trigger exceptions: The revert function can be used to flag an error and revert the current call. In the future it might be possible to also include details about the error in a call to revert. The throw keyword can also be used as an alternative to revert().
Вот ссылка на источник:
https://solidity.readthedocs.io/en/develop/control-structures.html#error-handling-assert-require-revert-and-exceptions
