A common mistake made in consumer apps is that user acquistion is seen as the key to success. It is true that you need to acquire users, but what you really need is a good hook and then to keep those users. Instagram's hook was that they made filters and sharing easy amd free. People wanted filters and the sharing part was a bonus. However, once they were there, they naturally had to take part in the social aspects which made it far more engaging and therefore they stuck around. After that, it is only a matter of time before others joined in.
User acquisition is a necessary but not sufficient part of success. So no, user acquisition isn't the key to success. And yes, you do need to engage your users and make your site/app sticky. But you can have the stickiest app known to man and it's completely useless if you don't have users. You need to do both and the only thing they have in common is being difficult.
