Silly question

For income

We are earning income BY sale of goods and incured expenses TO wards rent salries etc...

For B/s

We are raising funds BY loans and expend TO purchase assets.

You can understand the concept of "BY" &"TO" if you know the three golden rules of Accounts:

1. Real A/c- Debit what comes in, credit what goes out

2. Personal A/c- Debit the giver, credit the receiver

3. Nominal A/c- Debit all expenses and losses, credit all Incomes and gains

Also you should know how to classify a transaction i.e whether a transaction is a real A/c transaction or a personal A/c trns. or a Nominal A/c trns.

For Example: Mr. A buys goods for Cash

This is a Real A/c transaction & hence the entry will be -

Goods A/c Dr. (what comes in)

     To Cash (what goes out)

ie By Goods & To Cash.

Hope your Doubt is cleared

Just Like A Letter 

To is To Address

By is From Address 

Got IT :)