Return on Investment. Is what you get out of something worth what you put into it?
Investments can be time, money, heart, any sort of sacrifice, any transferance of something that has value to you into the project. For all non-economic investments, and for many economic ones, the assessment of ROI is subjective. The key is to recognize when something isn't returning to the enxtent that it has to for you to be satisfied, and decide what to do about that.