because... (very quickly)...
if someone says you are irrational and you can't trust your thoughts then what is to be done?
you can't suspend judgement on everything...
i mean...
descartes did...
but only for a couple days in his oven room...
the nature of the irrationality needs to be circumscribed...
there are certain situations where certain kinds of cognitions are not to be trusted.

if you are feeling intense emotional distress then it is probably best to suspend judgement on other peoples intentions and motivations, for example, because of the stress induced paranoia thing (limited and circumscribed failure in rationality).