In my (limited) experience, the graveyard of startups is full of companies that built products that never found product-market fit. The process leading to product is complex; First Round has published some of the best content that I've come across on product-market fit. What is far less complex, however, is the ability to measure product-market fit.
How do you know if your product that that "pull" with customers? Measuring it can be complex and misleading (although Superhuman seems to have a novel solution). Understanding it can be far simpler.
If your customers ask for a discount, and if you don't respond, do they come knocking on your door to somehow gain access to your product? If your service goes down, or if your customers lose access, do they reach out to you to regain access? Products that have a significant pull with customers almost always create a dynamic in which users are desperate to gain (or regain) access.
Do customers express their "heartfelt discontentment" with some of the shortcomings of your product? Customers tend to be ticked off only with those products that they truly need or want in the first place. For instance, I don't think anyone is truly ticked off about the shape, size and shortcomings of toothpicks at the dinner table.
Does the product offer some sort of a capability that customers didn't have before? For instance, I really like Apple's Airpods as they enable me to walk around easily while having a call. This creates a new capability that was not available to me before. If/when I lose Airpods, I'm quite likely to reorder.
Similar to driving a car with durable shock absorbers, you can typically feel when a product has a significant full.