Human nature is a very complicated thing and many times our emotions can rule our actions. I’m sure everyone, at one time or another, has had an awful day and snapped at someone at the office, on the phone or even over the dinner table.
Now, these instances happen in real time, where the interaction is not documented (unless there is a hidden camera at the water cooler). So if you make a mistake, you can apologize and smooth out the situation. Many times you can even improve on a poor first impression.
But when it comes to online interactions, it isn’t as simple. Your words last forever and can be seen by millions.