The argument is that most problems can be addressed in one of two ways. Either it's "Let's get this done" or "Ok, it's time to give up"
Imagine you're back in high school and you're standing at the start line for the 100 Meter run. Either you'll think "Ok, let's do this", or you'll look around, size up your competition, and think "What's an excuse for walking away".
Starting affords you the chance to realize what the essence of the problem you're trying to tackle is.
This in turn, allows you to course correct, and work on the right problem.
I think this goes for personal projects as well. Just try it, what else will you lose besides the time you'll likely waste considering your options.