What are the reasons why cash book balance doesn't agree with bank statement balance?

There may be some transactions which do not clear the same day hence balance does not agree. For instance:

- amount to be withdrawn from bank but could not be done due to bank timings same day. logically entry of same is recorded immediately & bank is not debited as withdrawal was not done same day.

- Charges levied by the bank in the bank statement not booked in the books the same day as statements may not get updated real time in system / Accounts books.