PhD interview - how to explain why I left a previous PhD? I previously quit a STEM PhD program after 1 year. The reasons were complex but included burnout, mental health, pressure from the industrial sponsor, lack of support and loss of interest in the project. 

Following some time out of education, I decided to reapply for PhDs. I have been invited to interview for a very competitive PhD program. It is stated in my application that I started a PhD previously, and I expect to be asked about this in the interview. 

The answer is messy and difficult to talk about - how can I explain it in the best light possible?
I'm not sure that explaining why you left is the most important thing. Questions might be phrased that way, but people really want to know what is different now so that they can predict that you will be a success this time. You can't avoid giving some direct response to the question, of course, but you also need to be able to point to things you have done since then that make your success more possible and more likely. 

Perhaps "loss of interest" was a result of lack of support or burnout. Both of those are easier to account for than lack of interest, I think. You needn't give every reason you can think of, but reasons that are fairly common and that have obvious corrective actions are easier to account for than others. 

Don't avoid the direct answer, but focus on what is now different.