Try this: Next time a new feature rolls out on Snapchat, put a kettle on the stove. By the time it's whistling, chances are an identical feature will be part of Instagram, WhatsApp, Facebook, or all three. That's because Facebook has been relentlessly copying Snapchat features over the last couple of years, to the point that, as Snap Inc. nears its public markets debut later this week, that more-than-flattering level of imitation is scaring off some investors.

The thinking is that since Facebook is so much bigger and more mainstream than Snapchat, its feature cloning will more likely than not succeed in limiting the smaller service's potential audience. It's a major reason some analysts are so bearish on Snap.

"It's worrisome," Paul Meeks, chief investment officer at Sloy Dahl & Holst, told Reuters. "Snapchat is going to have to continue to be really innovative and distinctive. It's going to be very tough to trump Facebook."

But in many ways, Facebook's "Single White Female" act only serves to highlight why Snap is such an intriguing company.

If Mark Zuckerberg's minions have sought to knock off big parts of Snapchat, that's because Evan Spiegel & Co. have proven time and again that they understand what young users want on their smartphones in a way no one else does. Snap's not looking to Facebook for its product roadmap but simply coming up with its own innovations. That's exactly why Facebook tried to buy its young rival for $3 billion in 2013.

"Facebook's interest in trying to copy Snapchat consistently...shows that there is something special," says Johnny Won, founder of Hyperstop, a tech consulting firm. "We just don't know how special it's going to be yet. That's what makes this whole IPO so interesting."

We saw this cycle play out with the release of Spectacles, Snap's wearable that can film short snippets of video. It's too early to call the glasses a success--they've only been available in limited release since November--but already Spectacles have drawn more mainstream hype among consumers than most other tech wearables. Naturally, there are now rumors Facebook could be working on its own version of Spectacles.

"Facebook has tapped into things that are cool for your mom and your grandma that we can all use together, but Snap has created something that you would find at Coachella," Won says. "There's a gap there."

Historically speaking, copycat behavior is usually a sign of a company that sees itself at risk of losing market share to a new foe. If you look back just one decade ago, Microsoft tried to follow Apple's iPod with the creation of the Zune. Microsoft was then much bigger, so, by the logic of the Snap bears, it should have won the mobile-music-player war. In reality, the Zune was an embarrassment.

The 2016 documentary Silicon Cowboys does a great job outlining how IBM tried to stop rival Compaq in the '80s and early '90s by copying the up-and-comer and ultimately failed. And Facebook itself had to deal with copying only a few years ago, when Google on multiple occasions futilely tried to break into social media.

"This is not the Silicon Valley ethos," Won says. "Silicon Valley has always been about the people who can truly innovate."