I see @MartinSleziak but I think why is it that there are some properties of a square matrix which always exists like eigenvalues of a square matrix exists irrespective of invertibility but inverse of a matrix cannot exists for non-invertible matrices that is there is some restriction? perhaps there will be some more generalized result which can say about the properties of the matrix more generally which may have been proved or may be proved if one finds the theme suitable enough.
I don't really know what to say to your last question, it seems a bit unclear and somewhat broad.
The fact that inverse of a matrix cannot exists for non-invertible matrices is basically the definition of invertible matrix, so that should not be much of a surprise.
its like why eigenvalues exists for any square matrix but inverse of a square matrix does not exist for any square matrix, is there any reason for that?
In one case the reasons is that there are counterexamples showing that the claim is not true for non-invertible matrices. In the other case the reason is that there is a proof showing that the claim is true for all matrices.
I am not sure whether you can expect some additional insights to this naive and simple observations.
@BAYMAX No problem. I have realized long time ago that I have problems in keeping up with younger generation.
@BAYMAX Probably the best answer is confused. I'll leave this question for somebody who knows more about this. If you wish, you can try also the new linear algebra chatroom.
@MartinSleziak I don't think that, a bit time ago when you helped me a lot in functional analysis and measure theory i was not able to keep pace with you :)