I may not be a millionaire yet, but I can tell you one stumbling block that might be universal: fear!
My first real estate deal took over six months from offer-acceptance to closing. I was putting in ALL the money I had and committing to what seemed (at the time) like a huge payment. I was scared as hell, and I admit to losing some sleep. Some days I honestly thought I'd rather lose my earnest money than go through with it.
But I have some very encouraging mentors, and they made all those feelings much easier to bear. I closed. I couldn't be happier.
Now I have a new problem!
The point is: don't give in to your fears. Trust the advice of the ones who have made it.