The short answer is: because I wanted to have my own lab growing up. To do so, you have to do your masters, PhD and PostDoc. There is a possibility to fast track to your PhD, as my boyfriend did, but you get the point. Most of the Principal Investigators (PIs) that I know that are getting their lab established have at least one PostDoc, and sometimes more than that. But anyway, it was my dream to one day become a PI. And so when my PI asked me if I wanted to stay for my PhD after I would finish my Masters, I didn't hesitate and accepted.
The thing is that, as I have stayed in academia for a while now (5 years in my undergrad program, normal length for my program; 2 years in my Masters and now in the middle of my 4th year of PhD) I've come to realize 2 things: I love working in the lab BUT having a lab doesn't mean you get to work in it.
I've seen several labs starting up and, at the beginning, while they get students, the PI will be working IN the lab, meaning doing experiments (the part I like). As time passes by and students start to arrive and settle, the PI will spend less time in the lab and more and more time writing grants (the part that I don't like). Suddenly you haven't lift a pipette in years.
Back to the question, why did I decide to do a PhD? Because I wanted to DO science, because I am so happy when I am doing my experiments, because it felt like what I was supposed to do to get to where I wanted to be. Do I regret going into a PhD now that I know that I no longer want to be a PI? Absolutely NOT. I am still happy with the path I've taken, even if I've had some issues with my experiments. Even now that I have 2 (very) different possibilities to pursue after I finish my PhD, this has given me a lot of experience and it is still part of the path that I need to go through to get where I NOW want to go, which is either Science Writer or Lab Associate.
I know, you are going to tell me that the first one means I won't be doing experiments and instead I will be writing. The difference here is that I would be writing to vulgarize science, which is something that through my PhD I've discovered and realize I really enjoy it. I could've only known this through all the poster and oral presentations I have done so far. I like sharing the results, I like discussing them. I do not like seeing how every PI around gets almost unreachable and quite fidgety when grant season starts; it carries a lot of stress obviously, because you depend on this to sustain your lab and your students, there is no fun in it, or at least from my point of view. As a science writer I would still get to learn about science and then make it more accessible to others, something that makes me very happy. As a lab associate, while I would still have to help with the writing of grants, there's still lab work being done. Doing experiments is part of the job description.
One thing I keep saying is this: if you are going into science you have to love it. But there is more. If you are going into academia, be sure you know what you are getting yourself into. A lot of people go into grad studies because "the pay increases with the degree". This might be true, but you have to think and keep this in mind, that education is a long term investment AND it takes work. I cannot speak for grad studies in other fields, but doing a PhD or even a Masters is not a walk in the park. There are long hours involved, being in the lab on weird days, a lot of frustration with experiments that might never work, and depending on the country, you might not have any financial aid and will have to deal with a job on the side.
Once again, I do not regret my decision. But I do know that is not a simple one and that is not a path meant for everyone.
Are you doing a PhD? Considering doing one? Leave a comment with your story, in the meantime, keep working on good science ;)