I think it's too easy to get it confused with K for king. N is descriptive enough that you know what it is, since the K in "knight" is silent.
Why abbreviation for knight is N and not Kt?
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You're the only exception, we call you kay instead of n
N is quicker to write and understand
In the old descriptive notation both N and Kt were allowed. Why only N in algebraic (i.e. why don't write Ktg1-f3 etc.)?