Penelope Trunk tells you not to change a career when:
You hate your boss
You want more prestige.
You want to meet new people
You want more meaning in life
You want more happiness
So when should you change your career? There's only one reason in my book (my yet unwritten book ;-) to change careers, when you have skills that you will utilise more and will earn you more in another career than your present career.
For example, I did my graduation in hotel management after school, thinking it would be great for someone like me who was people-oriented. This was self-diagnosis and in the early 1990s there was no real way for someone to get career counselling. At least, not in the small towns like Lucknow where I grew up. The other reason, of course, was that I was academically not bright enough to get into a good engineering or medical college.
So I did my bachelor's in Hotel Management from a place called WGSHA in the campus town of Manipal. After three years of studying hotel operations along with general management subjects- like Organizational Behaviour, Economics, Marketing - I graduated in 1994 and went for my first hotel job to a place called Aurangabad at a princely salary of Rs. 3000 per month. And you know what? I didn't like it.
So after 14 months I wandered into sales. I discovered I was great at opening sales but was lousy in closing it. So when I worked in Pharma Sales (in Agra of all places!) my sales figures spiked in the beginning and then died down.
That led me to realise that HR is probably what I should be doing. I observed the HR manager of my firm then (Eli Lilly) Mr. Sandeep Dayal, and I guess I role-modelled my career on him. Next thing you know, I quit my job, sat at home for 6 months and prepared for XAT.
I was finally a MBA in HR in 1999.
What if I had not found my calling in HR? A lot of people wander into careers because of external factors (family pressures, comparison with neighbours etc.) Some people don't realise that they belong somewhere else.
There are careers being made and unmade as we speak. If you focus on what you do well - then you will discover the right career for you.