As a consultant who has worked with several startups, I've seen a lot of startups focus all their marketing efforts on Facebook or Google ads, only to get shut down, sometimes without notice and on the whim of Facebook or Google. I feel like it is best to build both organic and paid customer acquisition channels as you don't have to place the future of your startup solely in the hands of Facebook or Google. This is what I recommend to all startups as well to help them weather any storm that comes their way and make sure that they survive through rough times!