commonly misused words up there, not their or they're :)
Some people are simply complainers, they live that way and will die that way. Don't know why exactly; perhaps they can't control "their" environment or some aspect thereof, so they complain all the time due to "their" perceived environmental inadequacy. For example, as long as foods are not all 100% organic, some people complain about it over and over again. Then again, some people need to release a complaint at least once and it rids them of the internal struggle.