It's much easier to decide specialize when you you are young (24-25 yo) and are still in dental school. Since you are used to living like a poor student, it shouldn't be too bad to continue live like this for another 2-3 years. It's not too bad to start making 6-figure income as a specialist at 28-29 yo. This was why I decided to do a year of GPR after dental school. I was afraid that if I made too much money in private practice, I would lose my focus on reapplying for ortho. Another reason for doing GPR was endo was my backup plan in case I didn't get accepted to ortho.
It's much harder for older dentists who have been out for a few years because they have to give up their 6-figure incomes and downgrade the lifestyle to living like a poor student. It's even harder if they have kids to support and their spouse can not find work in the state, where they get their specialty training at.
I didn't know anything about ortho when I applied. I was too shy to approach an orthodontist to ask him/her about shadowing opportunity. A lot of people in my class said ortho was the best specialty so I just trusted their jugdement. Since it was so hard to get in, it must be a good specialty to pursue. And of course, the most important thing was I wanted to make make more money as an ortho.
It was also easier to decide when the tuitions weren't too high 15-20 years ago. I only had to take out an additional $50k loan (tuitions + living cost) for my 2-yr ortho residency. Therefore, it wouldn't be a huge financial mistake if I had to go back to practice general dentistry (in case I didn't make good money as an ortho). Because the tuition was low, a 2-year program that charged tuition was actually more appealing to me than a 3-year propram that offerred stipend. I could easily make up for that by being out a year earlier. I was tired of being in schools for so long.....the shorter the training, the better it was for me. I was also in a long distance relationship and I didn't want to be away from my fiance longer than 2 years. Now that ortho programs charge much higher tuitions, picking a program that pays is obviously a smarter decision. But getting accepted to these paid programs is not easy....you have to have high class rank (which requires you to hard during your D1, D2, D3 years), good test scores (ADAT, GRE), and research experience (for ortho).