what makes a customer buy into a new idea?

Your initial question's answer is "if it saves them or gives them time or money, or speaks to their heart's desire."

Regarding metrics, I haven't heard anyone "moneyball" an idea, but I came up with the below off the top of my head. There are, of course, exceptions, but you're interested in a wide target. Everything listed below will keep an idea simple and easy.

• No more than 3 colors in your brand palette.
• No more than 2 words in the brand name.
• No more than 3 syllables in each word in the brand name.
• The marketing website or MVP will be simple (because it's new); Every web page should be accessible in less than 3 clicks/taps.
• All web pages should render in less than 3 seconds.
• The value proposition should be no more than 3 sentences and could be said in 1 breathe.
• A stranger to the idea should be able to navigate the website in less than 3 minutes, and know what the problem you're solving is, and how the idea solves it.

Every business and market is different. I would recommend the books "The Lean Startup" and "Tipping Point." "Lean Startup" discusses how a process of experimentation helps startups to figure out exactly what their customers want, when sometimes even the customers don't know. "Tipping Point" discusses all the large and small factors that can cause ideas, behaviors, and products to "tip" and become viral.

Does the new product/service increase the customers revenue, save them money, and/or decrease the risk of losing money? These are the key drivers from the top down of an org. That's always a key question to answer before building a new product/service. There are many more, but this is a good place to start.

Sure you can. Target the industry and product class, and then do research on the history of adaptation of new products or services in that market. This is all part of a business plan. Years ago, National research group used to have one of the most extensive and detailed databases. They measured and cross analyzed data for new movies so they would know how to market them. Now if you are talking about a completely new concept that isn't evolved from an already existent one...may be tougher. But the same idea applies.

A customer does not buy into a new idea. The customer buys satisfaction for his/her need(s). So whatever the new idea is, if it does not satisfy the customers' needs it has no place in their pocket. This is the beginning. If you go further, it will not just be satisfying the needs but also includes the mode of satisfaction and the manner of delivery and the environment of delivery. These are what your new idea should be addressing and not the customer buying into an idea that may not find a place in his/her need(s) satisfying basket.

Having loyal customers is all about attracting the people who share your fundamental beliefs. People don't buy what you do. They buy why you do it. This might seem obvious, but it's a critical step that is often overlooked. If you are the founder of your business, try telling your marketing team why you started it in the first place? Understanding "why" is essential to knowing how to communicate "how" and "what" you do.

Satisfaction from the product

Mindset. When approaching customers with a new idea, you got to identify early adopters from the back-benchers. Early adopters are those customers who are always on a look-out to try new things to improve their business, even if it comes at the cost of a bit of a risk. They are the low hanging fruits for your new-idea app. They comprise only a handful of all your target customer-base (probably 1 in 10), but they are incredibly catalytic in creating what's called the snowball effect, which would eventually also suck in the back-benchers among your potential customers. Metrics could be used to supplement your product pitch, but won't break the ice, unless you are presenting your product to an early-adopter.

On the contrary, in order to pitch your product to a lazy adopter and close the deal, you have to be patient, persistent and strategical and use marketing techniques like influencer marketing and social proof.

Curiously worded question. Metrics don’t drive adoption. They measure it.

what am I missing?

The question is vague, but it sounds like you're talking about idea validation, because the whole point of validation is to predict the chances of customers buying your product before actually building that product. Validation is not really a metric, but it can be quantified to a certain degree. In fact, I just wrote an article about quantifying validation: https://www.linkedin.com/pulse/what-exactly-product-validation-dimitry-rotstein/

Hope it answers your question.