When pitching to a VC it's not enough to say that your future customers want or even need your service. You have to assume that the people across the table know nothing about your space and as a result, they don't have a sense for sentiments and dynamics in the industry.  In order to get VCs to believe that there is a strong need for your new idea you have to make the case.

When you articulate this you need to keep in mind that most VCs want to invest in ideas that address a pain point. It's not enough for a service to be cool or just useful because it doesn't guarantee that enough people will adopt it - it needs to solve a problem. There needs to be some urgency.  In reality, these are often two sides of the same coin - the difference between a VC thinking that you are simply making life easier and addressing a pain point in part comes down to your presentation. Change 'everyone is going to be psyched to use this' to 'people are wasting time and losing functionality without this'. Focus on the pain.

Usually you can make the case with a few metrics. The best types of metrics quantify the pain: the cost of not using the service. Put this in dollars and cents if you can. If not, use the next best metric - time, megabytes, etc. If you can't put a metric on the cost use something more qualitative: survey results, analyst opinions, etc.

Just a few of these metrics can go a long way. They give the VCs something they can understand even as an industry outsider.

If you spend time preparing your case you'll spend less time making it.