Did you ever wish that someone would double-check your entries? If you did, your wish has been granted. There is someone keeping track of all your transactions. I can see that you are taken aback, "What? Someone is watching me over my shoulder?" No, this is not George Orwell's 1984 and Big Brother is not watching you. Relax. It is just your bank and your credit card company who are watching your transactions, as they should, and sending out detailed statements every month, again, as they should.

The double entry bookkeeping system of GnuCash does make sure that if you enter one part of a transaction, you enter the other matching part too. For example, if you enter a cash withdrawal of $300 from your bank and your bank balance is now less by $300 and you forget to enter an increase of cash balance of $300 in hand, the double entry system will make sure that you enter that too. However, if you forget to enter the entire transaction, the double entry system cannot help you. This is where reconciliation comes in.