I'm pretty tenacious and don't give up easily in general, which has led me to go down with several sinking ships (women and startups). I did realize I was involved in something special - the hard part was getting accepted to the program and for condensed matter physics, it was fairly straightforward to get your ph.d. (not easy, straightforward). Pick an exotic material, do a measurement no one has done and write about it.
I was unmarried, no mortgage or car payments and I had already completed 2 years out of an estimated 5.5. I just had to ignore my annoying advisor, focus and try to enjoy the cool, interesting parts of the science. I loved machining my own metal parts. And also I had to get away at times and try to have a life outside the lab. So, I decided to stick with it.
No regrets - I'm 44 now, and I admit I was fairly bitter about the experience for at least a decade after I finished.
The last thoughts are: Lot's and lot's of work. Can you be force-fed your favorite food 24x7 for 5 years and still like it? Like how Homer Simpson thwarted the devil force feeding him donuts?
I did have an office mate who worked 9-5, was a 6'2" former speed skating champion of Canada, wife and kid and was always planning to work for McKinsey and company, which he did after completing his Ph.D. in 4 years. Other people have different experiences. I was a hard worker, other people were brilliant.
Here's my two cents (I got my Ph.D. in physics from U. Chicago):
I went to grad school because 1) Chicago physics was famously challenging and I wanted the challenge, 2) Everyone else I knew went to grad school - I didn't know how to look for a job, 3) Chicago was a big city with good live music and nice architecture.
All were wrong - the only acceptable answer I believe is "I love science so much, I want to be a scientist for the rest of my life and nothing is going to stand in my way."
What happened was:
1) The challenge was 100x more than I really wanted. I found out early I didn't want to be a scientist, but decided I would stick it out like a perversely beneficial jail sentence.
2) I'm a very, very, very social person. Oops - big mistake. You don't make enough money to date. The mental challenge of living a lifestyle in complete opposition to my core personality was the most difficult challenge (5 years in a dark basement trying to detect light from single semiconductor nanocrystals). But, I found out I could take loans and moved to the artist neighborhood - punk rock, dating and beer helped. (Wine-women-song? Sex-drugs-rock n' roll?)
3) I met some of the most interesting people I've ever met in my life and that made it all worth while. I did some cool things and in the middle of the financial crisis I was able to make a career change because the Chicago physics Ph.D. superficially let me get my foot in the door.
4) I went to a NATO physics conference in Turkey, met a non-scientist woman and married her. Now I'm a capulcu.
5) Having a Ph.D. is a great conversation topic at parties.
6) I did some really cool science, but was exposed to many carcinogens and high voltage equipment at a young age.
My Dad was a Marine and I feel like I went through a Mental Marine Corps, no disrespect to the real Marines. Boot camp is not fun, but it turns you into a man of a sort. The first 2 course years were like a boot camp.
The financial impact of not entering the job market hits you even for years after you finish your Ph.D. You'll be behind other people your age for awhile.
My co-worker does the same thing. Thinks instead of opening the debugger. In fact, he never uses a debugger even though he's a hardcore low-level C/C++ guy. Another important thing is to have good logs. Don't log too much, but log the most pertinent info. Next he just looks at the code. If it's really tough, he adds a print statement or two. I've never seen him do more in 3 years of working with him.