Cryptography/Statistical Weaknesses

Letter Frequency
Whenever you consider any available language, it gives information about the frequency of letters that occur most frequently in it. The same matter is more enough for cryptanalysis (process of discovering ciphertexts) which is more beneficial when encryption is performed using the Conventional Classical Encryption Techniques.

This gives statistical information of data that cryptanalysts can use in order to decrypt the encrypted data, provided the language in which data is present is known.