Would you quit if you were waiting for a promotion, but promoted was someone else?

Quitting a job should not be based on being promoted or not, but being patient because it could be a bait or yard stick to check mate some traits in... you. You could aswell ask to know why?
 more

Is it normal to feel a bit insecure when you start a new job?

Very true, take some time to study your new environment , get acquainted with the do's and don't of the organization and turn your strength to... opportunities and your fear's to your strength. more

Could you advise some short courses or certifications to get a job?

I could, depending on the trending jobs and opportunities, interest of specialisation,, ability and capability and the background of the person.

Do you apply for the jobs for which you are under-qualified?

Sincerely yes, while I keep working on having information about the job

Yesterday I had a job interview and they asked me about my biggest failures at work. I didn't know how much honest I should be and what to say or not to say. How would you answer this question?

Honesty is the bridge, for every organization/employer's looks forward to having good and honest employee as their representative,so always remember... that your strength could be the source of your greatest opportunity and your weakness your failure but should be converted into your strength for a befitting reward.Thanks more

Should I quit my job if I feel overwhelmed and continuously stressed? Have you ever felt the same way?

You could ,if the working conditions, environment and the organization does not have your interest at heart and you are putting up your best to the... detriment of your health, family and life. Thanks  more