I’ve worked with hundreds of startups over the years, and not one company has stayed in "stealth mode" and won.
Clearly, those notions simply don’t hold up any longer, and, meanwhile, raising money hasn’t gotten any easier.
With so many startups competing for those dollars, imagine what would happen if they all stayed in stealth mode: How would they know whether an investor already had an identical company in his or her portfolio?
The biggest problem with stealth mode is that you aren’t showing your product and getting feedback from potential customers and partners.
As you build your startup, you’re full of untested assumptions about who will use your product and how.
If you build a startup in the open, people who know more about your industry can be valuable assets, bringing you knowledge about technology you need, and competitors you may not have foreseen had you operated in stealth.