Paradox of Outsample -Insample in Finance : Huge Implications for Investment and Trading Industry at least !

Unknown sample(Outsample) is also taken from known experience( insample)! 

Sampling of unknown based on known experience ! Paradoxical.

Can one take unknown sample from unknown experience then outsample should be anything of any period in true sense rather than specific choice based on known experience !! Paradox of Out sampling : Outsampling is actually insampling as usually done in finance world in particular !

Unknown sample is also taken from known experience ! Can one take unknown sample from unknown experience then outsample should be anything of any period in true sense rather than specific choice based on known experience !! Paradox of Out sampling : Outsampling actually insampling !

 If it were truly in principle it must work on any unknown unknown sample so called outsample not only selective outsample

Like if Convexity stregay works, it can possibly work in any unknown environment...unknown out sample size...this also differentiates true strategy from biased strategies which make specific choice of Outsample in insample way !

One takes say 80-20 because one knows from experience that this insample Outsample works...so this choice of Outsample itself becomes insample ?

How one decided 80-20 ? It's basically insample based on some known data....how can one know without known data or experience that 80-20 is optimal or good for example ?

If really Outsample then it would be completely unknown and any random sample size should be ok to be fit for Outsample in true sense...same for Insample.. So both Insample-Outsample pair(e g. 80-20) should be Outsample hence true for any random sample..otherwise not unbiased tether biased as insmaple...