B-schools teach you to be a good manager but not a good entrepreneur. An MBA course teaches you more about how to run an existing business than to spot an opportunity and start one yourself. To be a successful businessman, you need a different temperament.
Normally, students in a B-school are not from business families and, hence, are averse to taking risks. They should be encouraged to take up projects that will help them develop and hone their entrepreneurial skills.
If you are an entrepreneur in India, managing the business environment is a colossal task. To set up a business here, you need to get multiple clearances from various government departments. This is an area that is less addressed in B-schools.
In a B-school, you are taught collective bargaining on the assumption that the union leaders are responsible people and have the welfare of the workers in mind. This may not be always true.
For instance, we used to deal with a union with which we kept negotiating and nothing worked out for months. After which we realised that it was only interested in what it (the union) got and was willing to comprise on the workers' interests!
B-schools teach you to make a decision after detailed and logical analyses. But in reality, you may not always have adequate information at hand. Or you may not have the time to analyse the information.
Often you have to rely on your gut feel and intuition -- on your "sixth sense". Intuition cannot be a replacement for data and analysis but it can complement your scientific and rational thought processes.
At the same time, aspiration and passion for your work cannot be taught in B-schools. You have to discover it within yourself. Also, networking is extremely important for an MBA.