What is the most important thing your job has taught you?

I work at a hospital and my job is hauling around patients(mainly just pushing around beds between the X-ray and the wards) and I've just noticed that having a pleasant attitude and a perpetual smile on your face really helps.

No patient wants to see you with a frown. I might have problems of my own, but I'm essentially there for them and their problems usually dwarf my own. A smile really can lift their spirits, even if it might seem like an insignifgant thing.

I'm generally a pretty shy and socially awkward person and this realization has really helped me in my social life. Has anyone had a similar realization relating to their jobs?