Why outsource Accounting is difficult?

http://www.prlog.org/10084411-importance-of-accounting-outsourcing.html

Accounting is a critical department of every business and so it needs special care for its maintenance. Only a qualified and skilled accounts professional with depth knowledge can handle the work very efficiently of accounts business outsource process. The accounting task mainly includes back-office services and is works as a support staff to production and marketing team of any organization. Accounts department performs bookkeeping, general ledger, tax computation and filing, data entry, spreadsheet and statutory form completion and submission work.