That might seem common sense at first, obviously the future not having happened yet is subject to change. That said, predicting anything through the medium of ornate playing cards pretty much defies "common sense" on many levels. The observer effect states that the way we observe or don't observe something affects what is being observed. Considering this, isn't it feasible that the very act of trying to predict/observe the future influences the future?
The butterfly effect the observation that due to sensativity to initial conditions, the introduction of even seemingly insignificant variables to a system may result in major changes in the behavior of that system. I'd argue that it is precisely this principle which allows magick to work. While it is true that many acts of magick seem to depend on things which are not as subtle as the flutter of butterfly wings, elaborate ritual and the raising of enormous ammounts of mystical energy for example. I would argue that these activities are simply a necessary device that allows a far more subtle thing to transpire and it it is that thing which causes the actual magick. The mechanics of this subtle mechanism are largely mysterious but many astute observers have linked it to an alteration in consciousness. Consciousness altering experiences shouldn't be limited to the most common examples of drug taking or any number of mystical practices like Spares death posture. In truth the click of consciousness central to magick happens any time our conscious mind is distracted into ceasing its costant deliberation. Children at play, artists in creation all know that sense of timelessness. This sort of mental distraction is also the reason for the deeply symbolic nature of tarot decks. The mind becomes distracted sussing out arbitrary arrangements zeroing in on a single version of events. In other words divination is a highly effective way to cause the future to manifest in a specific way rather than being a way to read possible futures.
Any future event is a Schrodinger's cat, whether you are attempting to obseve the cat with the tarot, or attempting to use ritual to affect the cat in the box both of these seemingly different practices are way to "observe" the cat in question.
Getting back to those tarot layouts, we notice an unmistakably linear quality to them. However if we accept atleast the possibility that any attempt to observe the future will affect it, how can we be so sure that our attempts to suss out and explore the events of the past which are affecting our present are not similarly influenced by our observations? We can not directly observe the past and so it's Schrodinger's kittens all over again. Though it is tempting to point to our recorded history or even our memories as proof of observation, our very ability to look back at the way events were interpreted by observers in "the past" shows all too quickly how unreliable those observations are. In effect what we think of as the past, a collection of memories both our own and those of others committed to record are just the box in which the cat we call history is contained.
This may seem to defy common sense but then so does magick, so does the world of quantum reality, and yet in some subtle way way we know that these things are tied to and affect our common sense reality.
Considering all of this, it is entirely feasible to use divination in general and the tarot specifically for retroactive enchantment. There are any number of ways to go about this,the two most obvious are creating tarot layouts which imply the same sense of malleability of the past that they do the future. We can also stack the deck, which is is after all a pretty succint definition of magick itself.
Retroactive magick is an especially subtle operation. Whether conditioning or biology or both, we are predisposed to a linear view of time. This is important to keep in mind, because zeroing in one one future or past does not negate the other options, they are still just as real as ever. Our linear view is necessary for a variety of reasons, but our personal need to create a coherant history does not make other histories dissapear just because we are observing one specific history and not others.Even in the face of evidence to the contrary, linear perception is inescapable for anything more than brief moments. In Psybermagick Peter Carroll describes tricking your subconscious into believing that you will find a lost object in a place you wish to find it. He suggests that you can even pick a place you've already looked in provided you can make your memory of that search as hazy as possible. My own experience here shows that using places that are sort of chaotic like the inside of purse, or a table heaped up with "junk" are ideal places to use in this kind of work, another way to stack the deck as it were.
So combining the ability to manipulate our memory and adopting the belief that the past is malleable we can use the tarot to change the past to affect the present just as we might change things in the present to affect the future. In this case you'll need to make your memory of the events hazy as well as your memory of stacking the tarot deck in your favor. Any recollection of "the real past" durring this kind of work will short ciruit your efforts, as they constitute taking peeking into Schrodinger's box. This sort of work can be sort of confusing and disturbing and it is for that reason that adopting the belief that the past is malleable also serves as a protective measure.
Anyway, for the love of whatever, don't take my word on any of this, give it a try for yourself. And if and when you get it to work, ask yourself how much is possible? If you can use it to "find" you keys, can you use it to heal past injuries? If you can use it to heal yourself, can you use it to start healing the horrors of our common sense reality?
"The problem for scientists is that they are observing and trying to describe effects due to something which they refuse to believe can exist. The problem for magicians is that they refuse to believe that the effects they create or observe could be due to something for which equations could be written"- Peter Carroll