The security of private keys is paramount. If a private key is lost, stolen, or shared with someone other than its owner, then that private key is no longer a reliable factor in the creation of digital signatures. Human error can also be a problem for digital certificates. Inevitably, someone will type in a name or word incorrectly, and the resulting certificate will be questionable. Human error can be either intentional or unintentional in nature.
People give their personal passwords to friends and family.
People log into computers and then walk away, leaving the terminal unattended. People abuse their privileges and access forbidden information. All of these actions make technological systems open to criminal activity, which is intentional human error. Unfortunately, human error is a problem that has no good solution. By their very human and imperfect nature, people compromise the security of digital signatures.