We can therefore see that models are simply tools. Even if we forget to remind ourselves of that from time to time.

(1) Meeting desired target outcome
The 1st measurement therefore of the usefulness of a model is in terms of meeting an individuals target outcome .

We say individual, because a model can only be measured from starting with individuals and building up. A personal computer may be extremely useful for people living in a 1st world city, but totally useless to a bushman in Africa, with no access to electricity.

An explanation of how the planet revolves around the sun may be extremely useful for scientists tracking objects and planning space probes, but totally useless for a woman suffering the effects of a family trauma.

(2) Utility of a model
Most models today have a certain range of utility. That is to say that as our needs change, the model can provide a range of target outcomes.

We have kitchen appliances that are able to dice, slice, grate, heat, etc. We have watches that can tell seconds, days, months, years. We have cars that can tow a load via bull bar as well as auto control for long haul trips. Utility of a model is a measure of a model's usefulness in different situations.

Why don't we replace certain models when they don't seem to work?

Some models are easier to replace if broken than others. If a person has a faulty toaster, it is a relatively easy process.
Certainly if you had a broken computer and it was still under warranty, you could send it off to be repaired. If a light globe breaks, you buy a new one.

Similarly, humanity as a whole has shown it is prepared to throw out the old to adopt the new. In the late 1940's the city of Los Angeles removed its entire tram system is a classic example of "out with the old and in with the new".

So how come we don't do the same when we're not happy with a model of philosophy- such as a model of God, or of relationships, or of who we are?

The answer unfortunately is that overall, there hasn't been the shiny new replacement philosophy sitting in the corner store window.

Science for example, is yet to agree on a complete unified theory of the forces and energy. Few religions give physical road map directions to their version of heaven and while archaeologists have found the lost city of Troy, medicine is yet to fully show us what makes up our self consciousness.

No one has come up with a satisfactory model that links physics with metaphysics and ethereal concepts. Instead, in many parts of our life we are told to rely on "faith" and "hope". No wonder we get so stressed.