I find it quite difficult to agree with this statement based on personal experience. For me, it is quite easy to try things to see if they work which often leads to going round in circles until a solution becomes obvious. I found that when working with other people, it is a lot easier to put ideas out there and you usually get the weak points shown to you right away. Also, having said that, I am also finding that the most of my dev activity on my current project involves stripping out functionality that simply turned out to be unnecessary or half baked. I feel that having a co-founder would be great help in avoiding some of the unnecessary work in first place.