Error handling is the process of handling the possibility of failure. For example, failing to read a file and then continuing to use that bad input would clearly be problematic. Noticing and explicitly managing these errors saves the rest of the program from various pitfalls.
When an exception occurs, say an Arithmetic Exception then the current operation is aborted. Then the runtime system looks for an exception handler that can accept an Arithmetic Exception. Control resumes with the innermost handler. If no such handler exists, the program terminates.
Pallav starts with the most expensive option and ends with the best option with the Either monad.