Is A Midlife Career Change Possible In This Economy?

When is it time to give up on your dream of changing careers in midlife? That's the question Cynthia Hart, a former engineer, posed in a LinkedIn discussion. Hart wrote:

"I know many of you have made significant career changes.... and I know I cannot be the only one to feel I have 'failed' at trying. I was an engineer for 15 years. Very long story short, in 2007 I began an attempt at a career change towards environmental science, including obtaining a certificate, internship, and a Master's degree. However, after a lot of time, money, and heartache, I do not find myself truly any closer to my goal. After 5 years (and currently in an unrelated job that I had to take and do not enjoy) I feel about ready to 'give up'. Any words of wisdom for me? When do you know it's time to let go and move on? I'm not sure if it's best to go forward or back -- but I do know at this point in my life, a decent salary is necessary for me -- no more internships or graduate school!"