We constantly interact with everyone around us on a subconscious level; that interaction affects our moods, our decisions, and sometimes our outlooks on life. When you make the decision to exercise and transform your fitness, you become the subconscious inspiration for everyone you meet. There was probably someone in your life (a friend, relative, professional, etc.) who inspired you to attain the fitness level you seek. Sometimes it's no one in particular; you may just see someone at the mall and think “Wow, that person looks fit!” The next time you go into the gym, that guy or girl becomes a subconscious goal for you.
The same applies to you for others. Not everyone has the self-motivation to get up and go to a gym, go running, etc. But here comes you, determined to reach your fitness goals, and working to progress yourself as you train. Progress is the key word, because many people in fitness simply perform light exercises to maintain the fitness level they have.
That's not where inspiration comes from. Inspiration is that fat guy you saw at the gym 4 months ago who's burned through a lot of that bodyfat and added some dense muscle. Inspiration is walking toward a donut shop as you see someone else struggle with the decision to enter, but instead turn away for a healthier alternative. Inspiration is understanding that if the person before you was able to do it, so can you. Doing that for someone else in fitness feels better than reaching your own goals. That thought itself inspires me to train to the best of my ability.
So don't be discouraged because you only lost 5 lbs so far, or only added a half inch to your arm size. You are your own worst critic, so you may see how little you've managed to do, but someone else will see the changes you're making and begin to believe in themselves.
If you're unsatisfied with your accomplishments, the other person may feel discouraged. If you give up, you may not be responsible for someone else not reaching their goals, but you definitely have an effect on them. Take this thought into your next workout and realize the true strength potential you have. You'll probably surprise yourself, and inspire someone else.