From “The Mythical Man-Month” by Frederick P. Brooks, Jr.:

„The bearing of a child takes nine months, no matter how many women are assigned.“

 
This picture shall describe the fact that adding additional man power to a task doesn’t affect the schedule. This is true for tasks that cannot be partitioned.

 
In fact, I have seen projects were additional men were thrown in and the schedule got even worse. One reason for this is that the quality of communication goes down. But good communication is the single most important factor for the success of a software project.

 
If you sense problems with your schedule the first thing to do should be to find where that comes from. Consciously watch out for ways to improve communication. Always favor face-to-face communication over using a bug tracking system, instant messaging or email. See if there are other obstacles that get in the way of communication. Getting rid of unnecessary office walls or installing an additional whiteboard can have a huge impact.

 
Other ways to improve the quality of a team is to train the members, providing better tools and improving the development process.

 
Only then should you consider adding more resources in terms of man power. But remember that it will take some time until new team members come to full speed.

Finally I hold a copy of Frederick P. Brooks' book "The Mythical Man-Month" in my hands.
It was recommended to me from many sides.

"The Mythical Man-Month" is a book about software project management. What's so special about it is the fact that the first edition came out in 1975. From what I've read I would never have guessed that this book is over 30 years old. It is hard for me to imagine how software development was like back then. But, reading this book tells me that it wasn't very different. The issues and problems are still the same.

Picked from the book here are the five reasons of why programming is fun:

1. Sheer joy of making things, especially things of his own design.
2. Pleasure of making things that are useful to other people.
3. Fascination of fashioning complex puzzle-like objects of interlocking moving parts.
4. Joy of always learning.
5. Delight in working in a tractable medium.

Great!