Like most things, a prepare can only happen within a transaction. Jason
knows that this is necessary, and has made it so that the prepare starts
the transaction if it is not already started. I'll translate your code into
something you may be more familiar with:

>> with YourCar do
>> begin
>> Drive;
>> if not Door.Closed then
>> Door.Close;
>> <--- THIS MUST BE DONE BEFORE YOU CAN DRIVE.

However, normally you do not need to bother about telling a driver to close
the door before s/he drives the car out onto the road. Nor do you have to
worry about starting transactions in IBO (at least in a typical scenario
like the one you describe). In fact, in a lot of cases you do not even need
to prepare your statement - e.g. if you try to use ParamByName or First,
then IBO knows it has to prepare the statement if it isn't already prepared.

HTH,
Set