Nakira Vs Ma'rifa

[Imran]

AOA


اِنَّ الْاِنْسَانَ لَفِيْ خُسْرٍ

I've heard somewhere when Nakira(indefinite) noun is used instead of Marifa (definite) the meanings are increased/intesified in some way. The red word in the above Aya was given as an example.

What exactly is this rule? what is the way to identify it and what kind of increment in meaning it creates?

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