What is the line between quantum physics and classical physics .

at general what applied for quantum world not applied for classical physics , some people said CP is for big stuff whereas quatumn is for small stuff but where is the line where matter behave differently , where is the point where matter be like‏‏‎‏‏‎‏‏‎‏‏‎­: “oh sh*t we are in quatumn territory now , better behave differently?”