The world is too complex, and the range of actions required for any even a moderately complex project is too great, for one person to be responsible for it all. And even if one person is excellent at all of the actions required, he or she doesn't have time to do it all.
If you could do it all yourself, it's a technical project - and you should probably find a technical blog instead of this one.
You don’t need to be a leader to assemble a puzzle, unless it’s a 10,000 piece puzzle you are trying to assemble in a timed competition with five of your friends. You don’t need to be a leader to write a great book, but you need to be a leader to work with your publicist, agent, website team, etc. Unless you can do all of those things yourself, and you have that much free time...
This is why leadership is about relationships and not actions, about leveraging other people’s talents, rather than doing everything yourself.
Leaders enable those around them to do their pieces of the work more effectively.
They give people direction and momentum, and they do so gathering a vision from around them, by building the relationships required to make that vision become reality, and by changing their behavior to be more effective at those tasks.