In my opinion, there are two reasons why online businesses fail, one, the businessman does not have enough skills and knowledge to run the business (for instance, he does not have digital marketing and SEO skills), and two, he does not have enough money to run advertising campaigns.
Not having money to run some ads will be a major factor why the business will end up failing. As an online business person, you should be open to spending on ads and be hopeful even when you are not making the type of money that you wish to make at the start.