Mark is a very inspirational speaker, who can help to shift a person’s mindset in a positive direction just by listening to his infectious enthusiasm.
Which reminds me of the philosophy that you are the average of the five people you spend the most time with.
Another person’s attitude can certainly affect the way you feel, which can put you in a negative mood. Since it is known that there is power in thinking positive, then we know that a negative mindset is detrimental to achieving a goal.
If you are able to psychologically shield yourself from the negative attitude that is coming from another person, then that can help to protect you from acquiring a similar negative attitude.
Or if someone is constantly being negative, then you may consider avoiding them. Another suggestion is letting them know (perhaps subtly) that shifting their mindset in a positive direction will actually help their situation. (Especially in the case of a spouse or family member.)
In the process it will help you as well, and you can both incorporate the positive energy that is needed to reach your goals.