Overnight success is a misnomer because it's impossible to demonstrate true success overnight (or in a few years) as it relates to a business. Just the headline of this article should make a good argument to be wary of startups that appear to be doing too much in too little time.
If you invest a startup that claims to have been founded only 2 years ago and says to have already acquired so and so number of users, you might assume a certain velocity of growth for that company. If it turns out that the founders had unofficially invested 5 years of labor rather than 2, you just lost 60% value in your investment assuming the company valuation was somewhat proportional to their "traction."
The biggest question in a startups lifetime is "will they be profitable?" not "have they spent enough on Google AdWords to make it look like usership is going up?"
And in the very few cases where it's not, it's worthless as an example and incredibly dangerous to chase.
Put your head down, do the work, and enjoy the "overnight success" stories in a decade, if ever.