LOL. Please. Got any example of a success software project that doesn't have either one and is powered by Oompa-Loompas and pixie dust ? .... crickets chirping.....
How cash and manpower are applied over time is a factor also, but if have no cash and no manpower there aren't going to be any solutions.
I think what RobertMartens was trying to say was that if you have a software project BEHIND SCHEDULE, it's been proven that pouring all the extra developers and extra cash you have won't speed up the schedule.
This is because you don't need just warm bodies, but people who understand the code, the algorithms, reasons behind the algorithms, reasons certain decisions were made with the code, etc. This stuff is not written down during the development process, rather it only exists in the brains of the current developers, and the current developers need to stop what they're doing and explain things to the new developers, thus slowing down the current developers.
If the reason something is behind schedule is because of something external, like 'we don't have all Jonny Ive's buttons made yet' - no problem, someone can make the buttons, but if the reason something is behind schedule is because 'we can't get this to work quite right', then the new developer needs to understand (a) what is needed, (b) how it is currently working, (c) all the iterations of things that they've tried already and (d) side-effects of doing things certain ways. If the new developer doesn't know (c), then the new developer, if of the same mindset, will spin his/her wheels repeating previous failures. If the new developer doesn't know (d), then the developer might think he/she solved the problem, but caused a side-effect that harms something else, causing MORE developer time needed.
And communication issues are compounded exponentially with more developers. With just a few developers (4 or less), people will 'know' what others are doing by overhearing talk through cubicle walls, and by their day to day chat. More than that, meetings are necessary. More than that, or with remote employees, other communications are necessary, thus decreasing the development time.