Avoid flexibility!

On the project I am working on, the software should be able to do anything. It should be possible to make all kind of transactions, it should be possible to ad an unlimited amount of Mortgages (and to pay back an unlimited amount of Mortgages). The whole application should be unlimited.
When I came into the project, there was already a basis for this. The user is able to combine all kind of inputs (Transaction, ToPay, ToReceive, and some other things) all these inputs can have an unlimited number of items.
There is a difference between "design time" and "runtime". Design time is where the administrator can create models, by combining those input-designs and creating default items for them.
The runtime is when the design is used to make an invoice. The input-design becomes an input and the default item an item. I really liked this idea, but after some time things where getting difficult. One of the things is that inputs have dependencies, and different inputs have different behaviour for these dependencies.

In Holland we have some kind of tax which needs some money from a transaction and money from a Leasehold. But how do you know which transaction belongs to which leasehold? Ok we only take one leasehold and combine all the transactions, that is enough for this tax. But how do other inputs work with dependencies? and how can we make it as flexible as possible?

This is why I want to say, stop with this stupid flexibility! it only cost valuable time to implement things and make it possible for the user to do everything!

Flexibility is good and in software development it is very useful to have (without flexible code it gets difficult to add features to the code). But please stop asking for "everthing should be possible"-applications...