I see way too many people have killer skills to build something wonderful, but don't execute much when it comes to marketing. The reasons are plentiful: marketing is boring, it's a sleazy game, I don't want to spam people, I don't know how to, etc. That's why sometimes you see people that are good at marketing/sales out-succeed those that are great at building.
These days you gotta take people by the hand and bring them to your product (esp at the beginning). At worst, you're going to learn. At best, you'll get new customers.
Looking at what others are doing, I'd say it takes an equal amount (or more) of time and effort, to tell people about your product, as it does to build it. And it's a continuous thing, there's never an end to it.
So just like you develop the product and learn what it takes to build the best version of it, plan on telling people that it actually exists. You got tons of platforms for that. I've started Polyzag [0] to educate people (and learn myself), about how other profitable companies do just that.
It's a skill that you can learn, just like dev'ing.
P.S: Bonus points if you level up on marketing yourself w/o a co-founder. It's a superpower.