If you've ever seen a stranger behaving badly--a mother yelling at her kids in the grocery store or someone who's inebriated in public--you may have reacted by silently judging this person. At least that's my tendency.

But the truly wise resist this mental habit because regardless of how a person's behavior appears outwardly, you usually can't know his or her back story.

It may sound syrupy, but making assumptions--the nasty condemning type--truly are not good for you on several levels. Here are a few reasons why.

1. Making assumptions contributes to bad karma.

Last winter I accompanied my husband on a business trip to Chicago and made an impromptu hair appointment while he attended meetings. I didn't have time to walk the mile to the salon (plus, it was freezing) so I hopped into a cab in front of the hotel. For whatever reason, the cab driver appeared to be irritated by the mere look of me, rolled her eyes at the address I gave her and grumbled comments to herself that I could not understand. My initial reaction was to feel attacked and insulted at the unwarranted rudeness. Over the course of only a few seconds her behavior immediately cast a pallor onto my mood and threatened to ruin my afternoon. I could have assumed she was mentally unstable or generally just a bad person.

But then a myriad of crazy thoughts came to my rescue: "Maybe she just found out her husband was cheating on her and I look exactly like the woman. Maybe she has an incurable disease and is pissed at the world. Maybe her cat just died."

I don't know what her problem was, but I said a little prayer for the unhappy cabbie as I looked out the window. In doing so, the black cloud over my head dissipated. Then, I gave her an extravagant tip just to tilt the scales of karma in my favor. I left her vehicle feeling light and positive instead of offended.

2. Making assumptions mucks up relationships.

If you've ever been on the receiving end of someone making faulty assumptions about how you feel about something, you know how aggravating it is. It's akin to being wrongly accused of a crime.

I confess to doing this to my husband. I'll call him at work and perceive that he sounds busy. Unfortunately, the assumption I tend to attach to his busy-ness is that he's annoyed with my interruption and has no desire to speak with me. But every single time I complain about being disrespected in this way he denies being annoyed, but admits to being stressed when he happens to pick up my call. Does believing (inaccurately) that my husband of a quarter century does not want to talk to me, do our relationship any good at all?

Or maybe a good friend doesn't text you back in a timely manner. Do you ever start to wonder if he or she is mad at you for some reason? Most likely, it's life getting in the way. Yet, often people waste energy worrying about lapses in communication, instead of just asking about them.

3. Making assumptions is bad for your career.

I remember a boss of mine moving me into a role I definitely did not want. As an introvert, at the time I was more focused on building my writing portfolio, and less interested in coaching executives on their communication strategies.

I assumed my boss changed my role because he didn't think I had chops as a writer, was unhappy with my performance, or otherwise preferred my team members over me. Later--once I finally had the gumption to communicate my unhappiness with this lateral move--he told me the real reason for changing my role. It turns out he viewed my personality as well suited to working with high-level executives, whereas some of my coworkers didn't have as much of an aptitude in this regard. Of all his choices, he said, I was the best person for the job.

What I saw as a slam, he saw as a compliment. Once my faulty assumptions were demolished I was able to use the role change as an opportunity to build my interpersonal skills. Looking back, this has helped me infinitely more than remaining alone behind my keyboard.

I'd love to hear the lessons you've learned about the dangers of making assumptions.