There is no doubt that the single most important aspect to consider when buying a business is to be certain you purchase a business that is absolutely right for you as an individual.
It must be one that can thrive from your strengths and not suffer from your weaknesses.
Just because a business is doing well, does not mean it will continue with you as the new owner unless you match your skills to the right business.
At the same time, many floundering businesses can flourish under the right new ownership.
Certainly, there is a learning curve for any new business owner, and one must be prepared for that undertaking.
However, if the business is overly complicated, and has too many moving parts which require experienced oversight, or if the seller has simply built the business with their know-how overseeing every major aspect, the learning curve may in fact be too steep unless you have a wealth of related industry experience.
I have always felt that once a buyer starts to analyze a particular business, if they cannot explain it to others quickly and concisely, it is probably too difficult for them to ultimately grasp.
Most businesses are pretty straightforward, but there are ones that are complicated or have a wide array of components to them which can make the enterprise more cumbersome.