From my personal experience of over 10 years working with people from different industries and countries, the reasons differs and sometimes, what one considers a problem to quit or made the business to fail, some have managed to overcome and scale.
Some of the reasons below for business failure often revolves around inadequate market understanding (assumption is very costly), insufficient financial management (managing your finances), and the inability to adapt to changing market dynamics.
Lack of Market Understanding: Businesses may fail if they don't thoroughly understand their target market. This includes misreading customer needs, not identifying competitors accurately, or failing to adjust strategies based on market feedback.
Financial Mismanagement: Poor financial planning, misallocation of resources, and inadequate cash flow management can lead to significant challenges. Businesses need to control costs, manage debts, and allocate resources wisely to sustain operations.
Inability to Adapt: Markets are dynamic, and businesses that can't adapt to changing conditions may struggle. This could involve technology changes, shifts in consumer behavior, or responding to economic fluctuations.
Inadequate Marketing: Even with a great product or service, if a business fails to effectively market itself, reaching and retaining customers becomes difficult.
Understanding these factors and taking proactive measures can significantly improve a business's chances of success.
I will like to add that, you don't have to cross all the "T" and "i", failing is also a part of how you succeed in business. Some people quit too soon.