In nvarchar, I noticed that either we can pass a length of 4000 or the MAX like nvarchar[(n|max)].But I want to know the reason that why the limit has been put as 4000.Why not 5000 or 6000?

Can anyone please explain me the reason behind this.Thanks in advance.

I did a lot of googling on this, went through official docs also but not getting the actual reason.

And one more thing I noticed that when I am creating the table in. MSSQL it is allowing me to pass nvarchar(6000) but when I am trying to pass an argument in stored procedure of nvarchar(6000) then it is showing me error saying Invalid data type.

Why this weird behaviour?