Most available texts on spells and magic, due to a lack of knowledge [all spiritual and magical knowledge were removed and obliterated by the Christian Church], not only give wrongful instructions, but instructions that can also be very dangerous when working black magic, using death energy and other destructive forces to avenge injustices.
There is a great difference between evocation and invocation.
When we invoke energy or spirits, we create a link to the energy or spirit through ourselves.
Invocation also includes building up energy within one’s soul and discharging it through one’s aura and/or chakras.
This creates a tie to the victim.
Obviously, if one is using destructive or death energy, this can be very dangerous.
Most black magic spells that go wrong do so because of errors on the part of the mage.
There are other reasons for a black magic working going wrong such as the victim having a powerful aura that is able to deflect negative energy; the victim is under powerful spiritual protection [if one is under Satan’s protection, nothing can touch him/her], or bad timing on the part of the mage.
There can be other reasons, but the above are the most common.
Even white magick where healing is concerned can pose problems to the mage who invokes the energy before applying it.
Any time energy is invoked, a powerful connection is established.
Obviously, no one in his/her right mind would want to connect with a disease.
If the mage is working on money, personal power or some other positive application of energy, then invoking is desirable.
This also goes for love spells and workings of lust.
One must know the difference when working a spell, as ignorance or misapplication of the above can result in a spell backfiring or other undesirable outcomes.