According to one poll, getting on with co-workers is the number one reason to feel happy at work. In terms of job satisfaction and the work you do, fitting in at your workplace clearly makes a big difference.
Colleagues bound together, not just by the fact they occupy the same office or factory space but by shared interests and social experiences as well, make for more cohesive and effective teams with slower rates of staff turnover. Being a part of a group gives you more energy and enthusiasm and inspires creativity, as well as providing access to a ready-made social network with immense potential. If you don't fit in at your workplace, you're unlikely to be very happy or to stay there very long.