Surrounding yourself with positive people does not equal surrounding yourself only with people who agree with you. It means surrounding yourself with people who will not stand in the way of what you are doing and will let you have your own experience without nagging.
Someone who loves you, is going to tell you when they feel you are making the wrong decision. Someone who loves you is about your growth, development and long term happiness. Someone who loves you doesn't want to see you get hurt. Someone who loves you will balance you. They will let you know when you have gone out of alignment with what you want and attempt to bring you back in. This is not negativity, this is love.
We have to be careful to surround ourselves with friends and not Yes Men. Yes Men will agree with everything and will sit back and watch you fall. When they don't agree, they won't tell you or they may say something but give up easily because they don't want to be seen as negative. They don't want to fall out of grace with the inner circle. Once you do fall, they will leave you and become someone else's Yes Man.
All great thinkers and innovators surround themselves with people who will tell them the truth. People who will disagree with them. This disagreement is what brings about innovation. The debate allows innovators to see the holes in their ideas and figure out ways to solve them before the plan is executed. They become proactive and not reactive. The TED Talk below shows why disagreement is good.
Most people instinctively avoid conflict, but as Margaret Heffernan shows us, good disagreement is central to progress. She illustrates (sometimes counterintuitively) how the best partners aren't echo chambers -- and how great research teams, relationships and businesses allow people to deeply disagree.