"The most interesting part is that people actively choose which group they’re in through their actions. Some people come in the door and look for opportunities to get ahead. Others go in, watch the clock, do their work, and get their paycheck. Still others try to throw sand in the gears."
I did not understand meaning of "to throw sand in the gears" respect to above paragraph. Below is whole story.
http://www.thesimpledollar.com/14-tactics-for-getting-ahead-at-work-no-matter-what-your-job-is/