I have a lot of regrets. I had no debt because I was MD/PhD, but I spent 4 extra years of my life on that PhD.
I applied into rad onc residency, which seemed like a good idea at the time. I didn't realize that I wouldn't even get interviews at most of the places where they did the kind of research I did and wanted to do. Instead I matched at a low-tier place where they basically laughed at my research. It seemed like they wanted more MD/PhDs because it was prestigious, but gave no actual support for research. I applied for jobs everywhere when I was done training and had one offer after searching the whole country. The place was known to be malignant, but what choice did I have. Well turns out they lied to me about the job, and I got stuck 100% clinical at 3 different satellites for way less than typical rad onc pay. Everyone in the department is treated better than the physicians and turnover is high. The chair doesn't back up the docs at all and the department admin and clinic directors are downright hateful. I've spent years looking for a new job and I've gotten nowhere because the rad onc job market is absolute garbage.
My advice is to make sure you have an option to practice when you're done. Most people think if they can get through residency they'll have a good attending job on the other side. For me it was the opposite. Residency was pretty laid back. I've got another 20 years probably stuck in the same job I hate in the location my wife hates. Sure at least I can provide for my family (sort of, since cost of living here is very high) but even the full-time PCPs in this thread probably make as much or more than I do.