Call Provision - Purchase Money Mortgage

[Robert Littke]

I'm hoping someone can explain a Call Provision in a purchase money mortgage. I guess my question is, Why would a buyer accept a call provision as a clause? Wouldn't that put him in a terrible position when it comes due? Lets say the seller puts in a 5 year call provision, and decides to exercise it. Wouldn't the seller have to find away to come up with the balance? Or does it have to be a mutually agreed on exercise option? Thanks, I've gotten some great answers from this forum in the past!
Rob