That's why these RPs should be taken as group projects as well as something done for leisure. It gets tough, staying committed and all that. 

People have got to realise that it's not always going to be amazing and perfect. There will be stretches of time where the story is boring and a bit contrived. It's during these times that people have to ramp up their dedication, not scale it back. If you're only in it for fun, then doing something creative and collaborative is not for you. That's not to say that you can't have fun doing something of that nature. It's just that one has to remember that sure, it can be fun, but primarily, it's work! 

I have found that encouraging others encourages me in turn. So when someone feels bad for whatever reason. When someone doesn't want to post anymore. By all means, encourage them. Even when everything is fine, encourage them. Always be encouraging to each other. Always seek to encourage and inspire. After all, being good at that is truly the most important skill. Even more so than the supposed "relevant" skills. 

Also, one must realise that what one says can vastly affect the confidence of others. It's not always fun being the wearer of the pants but someone has to do it! Always be encouraging yes but call out bullshit whenever appropriate. 

It's work people! A labour of love! Not pretend play time! Start acting like it!