The safe combination may have been lost, may be locked inside the safe (it happens more often than you’d think) or the owner may have recently discovered that there is a safe in the home they just purchased and they want to use it (this is common with in-floor safes).
The best method to get into a safe when the combination is lost will depend on which safe you have.You can try to get into the safe by getting an override key, having a locksmith make a key, retrieving the code to the safe from the manufacture, breaking into the safe, or drilling the safe open professionally.