“The only thing that matters is getting to product-market fit.” 

Here is a list of my favourite quotes that pertain to the idea of product-market fit:

"do any users love our product so much they spontaneously tell other people to use it?"

"Plot the % active users over time (for various cohorts) to create a retention curve. If it flattens off at some point, you have probably found product/market fit for some market or audience."

"Survey your users and ask them ‘How would you feel if you could no longer use the product?’ and measure the percent who answer ‘very disappointed.’ If that percentage is over 40%, you have PMF."

Lastly,

“You can always feel product/market fit when it's happening. The customers are buying the product just as fast as you can make it -- or usage is growing just as fast as you can add more servers. Money from customers is piling up in your company checking account. You're hiring sales and customer support staff as fast as you can. Reporters are calling because they've heard about your hot new thing and they want to talk to you about it. You start getting entrepreneur of the year awards from Harvard Business School. Investment bankers are staking out your house. You could eat free for a year at Buck's.” — Marc Andreessen