Sure you are paying interest to yourself by taking a loan out this way, but there is a lot more to consider than that one positive.
A 401k loan is not "free money" and here's everything you need to know before you pull out a loan.

In really simple terms, 401k loans are not good loans.
They are different from collateralized loans (Think home equity).
If a collateralized loan functioned like a 401k loan the bank would come and break apart a room from your house and you would never get it back. There are significant losses.
Step back and evaluate how a 401k loan impacts everything you're doing.
Look at your whole life.
Loans, savings, insurance and goals all have to be considered before puling your money out from a 401k loan.