How do you keep from getting side tracked from business ideas outside of real estate investing? 

In my case, I started building a business, related to real estate, but it took me out of my core focus.

It all start like this: 

1. "how expensive X product or service is"

Then the following thought comes to mind:

2. "if I had a company that provided X or Y product or service I will save that money" 

It could range from getting a broker/agent license, becoming a general contractor, starting a flooring business, etc. Then as you start  dealing with nickel and dime customers, employees, lost inventory, learning curve, etc. I wake up one day to say:

3. "What the heck am I doing? I should be doing real estate investing not jumping all this extra hoops"

I know my thought process but I still fall in this trap every few years. 

What have you done to avoid this?