Interesting question, but I doubt anyone humble enough will be able to answer it in a few lines. I'll use an example from sports to answer: all baseball/soccer/football teams have the same amount of players (on the field) and the same roles/positions. They usually also have a similar amount of managers. Why then do some teams succeed and others fail? The answers are one, and most often a combination, of the below (the bigger the organization/team, usually the more reasons):
1. Individual talent (of the employees and/or of the managers).
2. Lack of experience (of the employees and/or the management).
3. bad fit of the business for the market (this could be a bad fit in general, or just at the present time).
4. (the manager) Not knowing how to inspire and motivate your team.
5. The manager's managers not knowing how to inspire and motivate the manager.
6. Not enough money (this is often used as an excuse, but can often be a legitimate reason - there is only so much a person can do with a limited budget)
Many excellent answers have been written on the subject, and I am sure that they are more elaborated that mine. A good start would be "The One Minute Manager" - it's old, a bit 'corny' and has some generalizations, but as I said: it's a good start.
I've successfully helped over 300 entrepreneurs, and I'd be happy to help you if you need.
Good luck