<aside> ☝ Building a business in these areas is possible. The biggest companies are even made out of these (Facebook, Twitter, Robinhood, etc).
As such, the following list is indicators of the businesses that are the more difficult to bootstrap. Don't necessarly discard your idea if you think you could easily go through these problems.
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[ ] Community-based companies / Social Networks/ Freemium models Much more difficult to monetize and requires high volumes
[ ] High entry barriers (1) - Legal challenges ie: industries highly regulated such as gambling platforms, cryptocurrency exchanges, digital wallets, etc
[ ] High entry barriers (2) - Saturated market Do dozens of companies try to achieve the same goal as you?
[ ] High entry barriers (3) - Difficulty to reach out to the targets of the product ie: Selling a product that has only the CEOs of Fortune500 as a target.
[ ] High entry barriers (4) - Business may interfere with particular compliance requirements Reformulate your approach to comply with data regulation and compliance measures
[ ] High entry barriers (5) - Businesses with licenses Gambling businesses / Fintechs (in some extend) / etc
[ ] High entry barriers (6) - Innovation in industries that are not responsive to it Have you contacted people from that industry to ask them if they are in favor of innovative products?
[ ] High entry barriers (7) - Large cash needed to start the company Could you build the simpliest version of your product without capital/ with limited means?
[ ] High entry barriers (8) - High-tech barriers (deep technology startup companies)
[ ] Nice-to-have products You need to find a business idea that solves a real pain. It has to be a "Must-have product". Not just a "Nice-to-have".
[ ] Lack of focus Make a SaaS that is doing ONE thing, but does it better than anybody else. Don't try to have 15 features that are not coherant once put together.
[ ] Being the first to do something
If what you do has not been tried/is not existing at all on the market, this might be a sign there is no demand.
[ ] No need to reinvent the wheel Don't do things differently just to be "more innovative" or "Different". Do it because it improves the value proposition and the customer experience.
[ ] "I created it because I would personally use it" approach
You're not the customer. Create products that are sellable. Don't create products you need but nobody else needs.