It's a hard world out there, and we need all the friends we can get, right?
But ... What if someone isn't your friend?
Here's a quick test to decide:
Likes spending time with you—and seeks you out
Makes you feel better about yourself
Offers support and congratulations when good things swing your way
Do you know anyone who failed this test? Is this someone you have regular contact with through work, social activities, or even social media like Facebook or Twitter?
Fire them. Or if you can't excise the cancer (hey, I understand--it's your sister and she's super competitive), at least tune it out.
If you want a positive life, you have to be a positive force. That means being a good friend or neighbor, opening yourself to good people and blocking the bad, and generally supporting others with love in your heart.