Definitely more than one. I currently have about 12 builds at various stages of completion.
I will simply get tired of working on one, lose interest and start on another.
Several are at a stage where the next step is going to require a degree of complexity and precision and I'm just not ready to devote the time and concentation yet.
Others I'm at a point where I have to decide which of several directions I want to go and I'm still indecisive.
Two kits have a major part I damaged and I'm not ready to spend the extra cash to buy another kit just for one part.
What is frustrating is I will get a strong desire for a new kit that is released, buy it, go "gangbusters" on it and then loose interest because of the next new kit!