Through friendship, people can check whether their opinions are right or wrong. One side of the good friend is the one who supports your opinion about your job or idea for running a business. However, sometimes excessive optimism would lead to negative consequences.
If somebody wants to run a business, they will need to be mentally supported. Nothing is better than a friend who can encourage you to pursue your dream. Take a software developer as an example, he or she wants to run an application that does accounting tasks fast and precisely. At first, people need some basic motivation to start the project. A supportive friend would encourage the person to start and agree with her or his opinion that an accounting application would bring major income.
While, people should not be biased with their opinions, and having an honest person who would mention the negative side of their opinions would be advantageous for them. In the above example, most businesses prefer to give their accounting tasks to professional companies with reliable legal backgrounds. Accounting has responsibility, and applications cannot cover and satisfy all of the requirements. So, having a friend mentioning the weakness of this idea is an absolute merit.
In my opinion, considering the balance around the community would be the key solution. Good friends are the ones who tell you the truth even if it is painful. Being negative and disagreeing constantly is not good either. Sometimes people have the right opinion about an issue, but not enough confidence to share it or make it real. So, agreeing with them and encouraging them would be all they need.