Have you ever been infuriated by someone's Facebook post?
You're not alone.
One minute you're mindlessly trolling pictures of your high school girlfriend's nephew's graduation, the next minute, someone's political post makes your head spin.
How could they possibly be so misinformed?
The right question is, why did I let this person into my head in the first place?
This lesson comes courtesy of my daughter's college professor, who told the class, "When you friend someone on Facebook, you are giving them permission to affect the way you think."
He said, "Every time you say yes to someone, you are saying I trust you enough to be intelligent enough and to be resourceful enough to come into my thoughts multiple times a day."
And with stunning clarity the professor summed up hours and hours of wasted human energy spent responding and reacting to people that we don't like, or even know very well.
The people who surround you (electronically or in real live life) affect your thoughts and moods. Their comments, opinions and rants occupy your brain space whether you realize it or not.
You've likely heard truisms like, "no one can make you feel inferior without your consent" or "don't take things personally."
But let's be honest, it takes a lot of mental energy to keep people out of your brain.
The better decision is not to let them into your orbit in the first place.
It's odd. We pay attention to the most mundane details about our life, but we're often unconscious about the people whose attitudes and opinions surround us each day.
And, it's not just Facebook where we unconsciously let "friends" into our brains without thinking; it's life.
When we take a job, we analyze the pay, the responsibilities, the advancement opportunities and even the commute. But how many people inquire about the office culture? When we're looking for a house, we calculate the square footage and critique the bathroom wallpaper, but how many people meet the prospective neighbors?
The truth is, we have a choice about the people who surround us. (I know; you can't choose family. See my past columns on patience, tolerance and heavy drinking.)
But when it comes to the second-tier people, the Facebook friends, the neighbors we sit beside at the pool and the colleagues we go to lunch with, we make daily choices that affect our well-being.
After hearing her college professor's sage comments, my daughter headed back to her dorm room and ruthlessly cut 500 people out of her mental orbit by unfriending them.
Her criteria, "If you're not doing anything positive, you're gone."
Thankfully, I made the cut.
To be honest, I'm impressed with her resolve. She said, "I'm really going to start thinking about who I surround myself with because it affects everything."
Whatever else she's learning at college, this lesson alone is invaluable.
Your mood, productivity, opinions and ambition are affected by the people you let into your life, and your head.
I find myself thinking about her professor's words again and again. When you say yes to someone -- be it on Facebook or any other social overture -- you're trusting that person to be intelligent enough and resourceful enough to enter your brain.
It's your head; it's your choice. Choose wisely.
Lisa Earle McLeod is the author of several books including "Selling with Noble Purpose: How to Drive Revenue and Do Work That Makes You Proud."