This is a great question, Elmirza! 
You've got the right idea pushing yourself to finish the story to show your friend. The best friends a writer can have are the ones that care about your stories and getting to read them when they're done. Part of why I started the weekly and monthly goals threads was to inspire us to write by telling others that we are and having them encourage us to finish. 
Aside from accountability partners, I'm also inspired by seeing other's get published. You can get published, it just takes time. So, seeing others accomplish that goal helps us realize it isn't impossible. It's also worth mentioning that setting realistic goals en route to publication is inspiring because it shows you can achieve the steps needed to reach the ultimate goal. 
Listening to interviews of authors who've made it is also inspirational. They can share advice that, even if not applicable to where you are in your story at the moment, still sets the mood of being in the company of those who want to succeed in writing. That atmosphere is contagious and great for inspiration. Just make sure you take advantage of it and get writing before your mind is distracted with other desires. 
Another question I think bares discussion is what or who inspires us to write when we're afraid. For me, knowing that I've finished a book motivates me both through confidence and the joy I remember feeling when I finished. My second book was easier and better, but still had moments of fear where I didn't know what to write. If you are afraid of what to write, sit down and brainstorm what conflict is left unsettled, and if there isn't any - make some  

 Then have fun with your conflict and finding resolution. Writing is all about conflict and resolution, and the adventure in between. 
Lastly, the tool 
Write or Die motivated me like no other. Anyone who hasn't heard of it or tried it really should. It's free, and you can do it online without downloading.