I got this idea that as a natural defense mechanism the various types have to adapt and create a shield of another type when their natural type is not nurtured. And naturally, I realized that this can be both positive and negative.
The central idea is in the following example.
Take an example of INFP.
INFP is Fi Ne Si [Te]. When the Fi+Ne (supported by Si) fails to create a positive result, Fi then takes a backseat and the unconscious Te steps up to take control. But Te being unconscious needs a function to direct it. So something must go before the Te+Fi combination.
The choices then become Ni, Ne, Si, and Se. Now I'm not a firm believer in the shadow function aspect of MBTI and it seems most aren't either and that no one has a good model of what the shadow would even be for the different types. So from my observations an introvert does not become extroverted when under stress (although they may act out in frustration which I do not consider as being extroverted, but simply a natural reaction of stress). So this leaves Ni and Ne. And since the INFP needs an introverted function to direct their Te it seems natural that Ni will feed their Te.
Then what we end up with is Ni+Te (supported by Fi taking a backseat but still watching over and making sure everything is still in line with values).
And taking this a step further we could say that doing such a thing successfully for an INFP is a healthy mental shield to exuberate and grow for tackling problems their conscious psyche is not able to do successfully and as well.
And then it would follow that their can be an unhealthy way to shield oneself. In the case of the INFP, I decided the worst thing this type could do is try to invalidate and throw away their Fi when nothing about it is being successful - relying on Ti to lead instead of Fi and becoming unstable and neurotic like a cat thinking it is a dog, and vice versa.
<attaches suit of steak armor to naked body>
Okay, Pedro. You can open the lion's gates now. I'm all ready.