this is my private opinion:
1.looking for a better job with well pay
2.too much pressure to continue their work,probably it's just their first work experience,they can not adapt to so much work immediately
3.bad job-choosing attitude,maybe they think the job they do now isn't fit for their literacy level,this is what many university-graduates think in their mind in China
4.a bad-tempered boss
5.belibeve it or not,somebody do it just for fun
6.need different job experience
7.the teenagers borned in 80's always try to be different from their parents,they don't think it's right to stay in only one position in their life.