Pinterest has banked its business opportunity on serving as the “productivity tool for planning your dreams”—in normal human words, a discovery tool. But in contrast to other social media platforms, the company has never had a big advertising business. Now, as it plans to go public, it is attempting to reverse this reality, introducing a number of new ad units, some of which are focused on video ads.

Video ads, like its predecessor, TV ads, are mostly considered brand advertising vehicles that help build awareness at the top of the funnel. While most modern brands’ marketing strategies put the most money into direct-response and other trackable ad formats, rising prices are pushing them to embrace an increasingly diversified marketing mix that includes more brand advertising, even if attribution is harder.

Facebook, and specifically Instagram, is in a much more enviable position than Pinterest. Its robust marketing business was mostly built on selling highly trackable ads that allow brands to see the correlation between ads and their conversion as best as any ad unit can, while also offering more brand advertising options as needed. Instagram has become the number one platform brands are investing in social, and the mix of organic posts with promoted ones has given them a powerful toolkit to grow on the platform. The more recent introduction of product tags, which allow brands to highlight products in both organic and promoted posts and Stories, helps drive more precise conversion. And now, with the introduction of Instagram Checkout, which will allow someone to discover, consider and purchase products without leaving the platform, Instagram has assembled the most robust advertising funnel for brands.

In comparison, Pinterest’s primary focus on discovery looks meager. As the company admitted in its S-1, “planning your dreams”—whether that means buying a house or purchasing a wedding dress—is inherently aspirational. Making them reality takes time and money, if they happen at all. This puts Pinterest in a unique position among social platforms: It is aiming to monetize attention, as Facebook and Instagram do, but it doesn’t have the right type of attention to monetize since it’s so disconnected from any consumer activity that could lead to a purchase.

This hinders the ability for brands to attribute success to and capitalize off of Pinterest, which reduces the likelihood that they will invest more advertising dollars in the platform. The last-click nature of attribution—meaning that the last advertising channel a shopper encounters before finalizing a purchase typically gets credit for the sale even if she was influenced by other ones beforehand—hurts Pinterest’s chances further. Even if a shopper was first inspired by the product on Pinterest six months or three years ago, Pinterest will likely never receive a penny for its efforts. The faster a user converts after seeing a given ad unit, the more that advertising channel can claim its worth. Pinterest introduced Buyable Pins in 2015 in an attempt to enhance its value, but the effort failed because consumers were not looking to buy directly on the platform.

Though Instagram and Pinterest both launched in 2010, Instagram tellingly waited until 2018 to add product tags, while Pinterest tried three years earlier. Instagram’s patience proved advantageous as it incrementally encouraged users to behave in ways that would make such a feature successful and ultimately made users comfortable shopping on the platform. Pinterest, on the other hand, launched product tags without establishing the necessary underlying habits first.

Pinterest may be able to build a small advertising business for itself, especially among consumer brands, but it will likely have a minimal effect on the market because of Instagram’s headway. Advertisers vote with their dollars, and the results are already in.