First principles are concepts and ideas which are timeless.
They are true now and will be true into the future.
First principles are highly work learning because when you master a core principle, you have it for the rest of your life.
This makes learning core principles much more valuable than learning specific products or ideas which are not based on fundamental core principles.
I think of concepts in terms of how long will this concept be correct and valuable? Like it’s ‘half life’ - 5, 10 years into the future how valuable will this knowledge be?