When you are writing an app as an indie, you don’t have that same motivation. As a software developer, riches and fame are in no way guaranteed. Your motivation has to come from within because external motivations fade too easily. When you are struggling with a complex pattern or bug, knowing that the effort it takes to find a solution might make money several months in the future is horribly weak incentive. It won’t drive you to pull an all-nighter or push through days of feeling like an idiot.