I get asked a lot about what I think is the most important ability for a tester to have. Some people are going to argue technical knowledge; others are going to argue logic; others still are going to argue negotiation skills. While all of those are important, there is one skill above all that is vital for survival in the software testing industry...the ability to control your emotions.
Note that I said "control," not "suppress." If you suppress your emotions, you're just going to make yourself sick. But if you can control your emotions and keep them from taking control, you will survive.
Why is controlling your emotional state so important for testers? Well, our entire job is essentially to find fault in the work of others. As a result, you will be called a liar, a hack, a worthless piece of human debris, a developer wannabe, unskilled, unwanted, a waste of money, a waste of flesh, a waste of your father's sperm, dead weight, and a pathetic excuse for a human being...and that's by the people who respect your opinion. There are others who will do much worse. It's not uncommon for a software tester to get in at least one fistfight during their career, unfortunately.
So you have to be able to control your emotions while you are dealing with non-testers, but you also need to be able to vent your emotions afterwards. I've left meetings and burst into tears. I've known testers who have left meetings and put holes in walls. Emotions run high in this industry, and the only people who will say otherwise are selling something.
Most testers try to suppress these emotional urges, but all that does it shorten their careers. You can only keep something bottled up for so long before it leaks out, either as an ulcer or a violent career-limiting move. The hardest job for a test manager is to identify when a tester is suppressing their emotions, pull them aside, and let them get it all out.
As an industry, we like to think that the process of software creation is clinical. We posit to outsiders that our architects design our software to exacting specifications, our developers build using the highest quality tools, and our testers are there to ensure that our software works. In fact, the "design" of most products amounts to scrawls on the back of a napkin, most developers cobble their work together with a hodge-podge of mismatched tools that barely work together, and testers are thrown at a project like hamsters being catapulted against a brick wall in hopes of breaking it down.
Our industry is as much chaos as science, and as such, emotions are a factor. If you ignore the emotional impact of your employees, you do so at your employee's and your customer's peril.