Value Your Time AND Your Money
Since real estate investing is an active business model, you need to give value to your time and money when you are looking at deals. You need to make money based on the time and money you put into it.
That means looking closely at what you're going to get out of a deal based on the amount of money you put into it. For example, a $15,000 return is a great deal when you put in $15,000 in but not so much when you put in $100,000.