Negativity can ruin the atmosphere faster than a can of freon, mostly because being around gloomy people is a miserable experience. One guy used to ask why I never invited him to play basketball with me. He’d see some of my friends shooting around and comment about how he hadn’t been included. Later that week, if I asked how things were going, he would mention that things would be better if people didn’t exclude him all the time. So why didn’t I invite him to play basketball more frequently? The answer is pretty clear. Not only was every interaction with him sour, he clearly did not like me.

Before you complain about how “there are no attractive women at Harvard,” recognize that it sounds a lot like, “women don’t want to date me, so there must be something wrong with the women.” The trouble with being negative is that you come across as bitter. My most romantically successful guy friends rarely find fault with their love interests, even after rejection, and my smartest friends are the least likely to grumble about a bad professor or an unfair class. No one misses the fact that you are trying to justify your failure by blaming someone else.

So develop a positive attitude. When you’re going over your midterm with the course assistant, don’t take the attitude that you’ve been wronged. See where you may have messed up, or if you were right, then recognize that the error was accidental rather than malicious. Give people the benefit of the doubt, and assume that they will do the same for you. Don’t criticize other people’s trivial quirks, and don’t apologize for yours. When you wear a new outfit or tell a new joke, own it. If it doesn’t go over well, work on your delivery, but don’t lose faith in your style.

When you come across other successful individuals, don’t mark them as competitors, they are your future friends, resources, and collaborators. When you meet people, bring some energy to the table, tell them about the things you find exciting, and let them share your enthusiasm.

You don’t have to be the liveliest, bubbliest kid on the block every day of the week. We all have moments where we really have to force that smile, but rather than dumping your complaints on those around you, spend some time with yourself. If you don’t have the energy to go out, then don’t. Take the opportunity to finish up that paper on whether performance-enhancing drugs should be allowed in professional sports.

But when you feel good, let your words and body language show it. When I pass you in the hallway, smile like you’re happy to see me. Dale Carnegie will wax poetic about how smiling opens up all sorts of business opportunities, but the truth is you’re so much prettier when you smile. When we’re talking over coffee, look me in the eye like I have your attention. Wave and shout to me from across the field, and when you walk between classes, walk like you’re on a runway.