Indeed mindset is key to controlling what is happening within us. Our thoughts and feelings become negative when the situation around us tries to hold us back from what we love to do. For example one is a soccer player, and a severe harmstring injury holds him out of playing for 6 months. The mindset will be key for he's returning to play the game. If it's negative, he'll not recover in time or he's career even completely getting shattered. But if the mindset is positive, he'll break the barriers holding him and recover in time.
Let's avoid any sort of negativity around us, from friends, different conditions among others.