Magick is often cloaked from public view for myriad reasons. First, many are nonbelievers and those drawn to magick surely respect the opinions of those from different faiths. Nonbelievers and their skepticism may also bring unnecessarily negative energy into a working and either render it ineffective or change the intent and cause a misfire. One school of argument, often seen with voodoo or hexing, relies on the subject’s awareness of magick being carried out on them. Magick used for the direct manipulation of another person has much potential to end up hurting the spellworker if used unwisely, and perhaps enmity is best expressed in one’s own heart that positive energy may be radiated outward into the world. Keeping an enemy closer than a friend requires a certain element of trust.
Finally, any spell, casting, or ritual that has been made public comes under the scrutiny of anyone aware of its existence, whether for good or ill. In the case of a coven working in unison, all members are acutely practiced for the task at hand. Unlike the generalized prayer requests in times of illness or strife, a spell is typically much more thought out and planned.
If someone disagrees with your working and decides to work against it, you may both be caught in a battle of wills that no one ends up winning.
Clandestine Ritual 