what's up with the pixies

ok, it has been 2yrs since by big chop. And now I have little knots in my hair called pixies. i'm trying to understand why I have them. I have searched all around the internet for answers and what I see is No one really knows why we get them. My understanding is that they come when your hair gets tangled, makes since. But then i came across a forum that was talking about the scissors you use. If your scissors are dull then your hair have more pixie knots.I can say that the time frame from my big chop(may2009) till oct 2010 I did not have any pixies and my hair was cut by a pro. Around oct I wasn't able to take care of my daughters or my own hair because I was sick from being pregnant. After that I noticed our hair had pixie knots and when I cut them It seems like alot more came. So I think tangles may have started them but now the fact that I trimed my ends with dull scissors it made more. I looked at a ad for splitender and I saw some reviews from other naturals and I think I might want to try it. Wish it wasn't so much money but I really want to see how it works.