Unfortunately there really isn't a conclusive reason why anyone gets ITP, that's why idiopathic is the first word in the acronym. Idiopathic being defined as relating to or denoting any disease or condition which arises spontaneously or for which the cause is unknown (thanks google). This might be off topic, but this is why I hate when doctors refer to I in ITP as immune because it gives the sense that we know more about it than we actually do. There is however plenty of speculations and statistics that we can look into. For example, women (born as) are more likely to get it than men. Doctors believe this to be due to the hormone fluctuations they go through. The most prominent example would be pregnancy, which is a viable reason to get ITP, women's hormones are at an all time crazy. It is also seen that girls going through their teenage years (puberty) are likely to get it if they are going to get it. Another important aspect about any autoimmune disease is the likelihood of getting another one. When I finally went into remission with my ITP, my doctor made it very clear that I had a pretty high chance of my ITP coming back or contracting a new auto immune disease in the future. While it sucks, this is what comes with the territory of autoimmune disorders. There are also some sources out there that speculate viral infections can cause ITP, particularly in young children. I have yet to meet anyone who actually fits into this category, including myself who was diagnosed at a very young age. There are also the people who claim that the MMR vaccine can cause ITP, however numbers show that you are more likely to get ITP after contracting Measles, Mumps or Rubella than those who show symptoms of ITP after getting the MMR vaccine itself. If anything I am saying is sticking with you, it's that there really isn't one known cause. Doctor's can't even come up with a universal method of treating ITP some saying go the IVIG route, others steroids, and god knows what else they want to put in you. So if anything, i would stop focusing energy on how you might have gotten it, even though it's tempting, and start thinking about treatment plans according to the severity of you're ITP.