Suppose we have a hash-function (not a secure-hash)
   h(str) = the ascii value of the first two letters, added together.

   h("AB") = ascii('A') + ascii('B') = 65 + 66 = 131
   h("CDEFG") = ascii('C') + ascii('D') = 67 + 68 = 135
   h("AB") = h("ABC") = h("ABasd;jfsa;;asd;fas;fjk;")
   h("DD") = h("ECASDFSDF")
   h(" &") = ...
   h("DD") = 2*68 = 136 = h("BF")

Okay, `h` is a pretty lame hash-function -- not a secure-hash.
BUT sha256 is a much better hash-function.
Are there two strings that both hash to the same result, using sha256 ?

  YES -- there are   16^(strlen( hash('sha256','hesdfasd') ))
     ~ 1.1e77 possible results, from sha256 output.
  But an infinite number of strings.
  So by the pigeon-hole principle, there are an inf. number of strings
    which all hash to the same result!