Financial accounting is based on the premise that the transactions and balances of a business entity are to be accounted for separately from its owners. The business entity is therefore considered to be distinct from its owners for the purpose of accounting.
Therefore, any personal expenses incurred by owners of a business will not appear in the income statement of the entity. Similarly, if any personal expenses of owners are paid out of assets of the entity, it would be considered to be drawings for the purpose of accounting much in the same way as cash drawings.
The business entity concept also explains why owners' equity appears on the liability side of a balance sheet (i.e. credit side). Share capital contributed by a sole trader to his business, for instance, represents a form of liability (known as equity) of the 'business' that is owed to its owner which is why it is presented on the credit side of the balance sheet.