In an interesting blog post Nick Farrell asked a pivotal, and yet frequently ignored, question about why some magic fails. He cited a number of reasons people have given over time, including classic cop-outs like God or your Higher Self saying no, and the more acceptable notion of psychological blocks.
On the first topic, I do not personally believe that God or the Higher Self would refuse a request. This might be an acceptable idea in a devotional school of thought, but magicians do not simply go with the flow—they create and direct the flow. A magician is an active player in the universe, one who takes responsibility for his or her life. If a ritual for a job is performed and it does not work, then the magician cannot simply blame God and accept this as "the way it is meant to be." Such fatalistic thinking has no place in magic.
So if external forces are not stopping us, that leaves internal forces. In many ways we are our own worst enemies, and part of the process of the Golden Dawn system is to tear down the poorly built construct enforced on us by society, our own Tower of Babalon, and build in place something with a stronger foundation, a "self" designed and moulded by us as we see fit. Of course, this is no easy task, and this is why we employ powerful occult symbolism and forces to give us an advantage in the battle with our own minds.
When a ritual fails, then, there is certainly an element of us blocking the result. We might wonder why any of us would block a result like winning the lottery, but these are usually deeply rooted subconscious blocks, the kinds of things people spend their entire lives trying to sort out, while others remain oblivious to them. Feelings of guilt or inadequacy could unearth the seeds of prosperity that are sown in a ritual, while doubt and frustration, and even the "lust for results" can cause a constant blight upon them.
Nick raised the point that this explains why his own ritual for himself might fail, but why does a ritual performed by another magician for him also fail? The same issues apply, but there are additional factors. Firstly, the manifestation is sought within person X's life, so it does not matter whether person X or person Y does the magic; it still has to go through the conduit of person X's world, where it can be assailed by all the various destructive elements of his or her psyche. And even if it manages to bypass these, person X might be in such a negative mindset in regard to the desired outcome that he or she could actually be ignoring the opportunities that are arising as a result of the magic done.
Let us use an example to drive this point home. If Bob does a ritual for wealth, but is unsuccessful, and then asks for the help of Jane, but then Bob refuses to accept a job offer or go to that social event where he would have met millionaire Tom, the issue is not that the magic has not worked, but that the resulting opportunities have not been taken. This might be through the same feelings of inadequacy that stopped Bob's ritual from working in the first place, or Bob might be so immersed in his financial issues that he not only does not see a way out, but his frustration blinds him to any doors being opened to him.
Of course, the problem with this idea is that it is hard to prove, because we do not know for certain what would have happened if any available avenue was taken. Attending the party might have led to Bob meeting Tom, but there is no guaranteeing they would have become friends, or that Tom would have offered Bob a job or paid off his debt. Missed opportunities are generally, by their very definition, things that have slipped under the radar, so it easier to simply think a ritual has not worked.
There is also the issue of whether or not a ritual should be left to its own devices or constantly reinforced. While there are various schools of thought on this, I think a middle ground approach is the most effective. When a ritual is performed, there is a "gestation" period immediately after, and ideally the magician has set a time frame for the result to become manifest, by which time he or she can judge if it has succeeded or failed. During this period it is important to let things happen, not constantly check to see if they are happening. This is the "To Keep Silent" part of the Powers of the Sphinx. The reason for this is that we performed the ritual in our magical mindset, but we usually "check in" later with our mundane mindset, which has the tendency to question, doubt and otherwise undermine our efforts. The fact that we need to check at all means we are unsure if it is really doing the job, so immediately we are smothering the seeds with doubt, or prodding at the earth with questions, potentially unearthing the seeds completely.
To balance this approach, however, we need to consider that once the gestation period is up, and if the desired outcome has not manifested, it is senseless to simply give up. The ritual, a variant, or something new entirely should be employed. If the desired outcome is monumental, then we must make an investment on a similarly large scale, potentially a long-term magical operation. Perseverance is the key to success in any aspect of life. Those who stop climbing the mountain halfway up will never reach the summit.
In the end the elaborate rituals we employ are largely designed to bypass the parts of ourselves that doubt our abilities or attempt to hold us back. Instead of using language like "I deserve X," we employ symbolic language that does this on a much more primal level, tapping into the very essence of not only our own being, but that of the universe at large. There such seeds can grow into manifest results, in much the same way we consider the Four World of the Qabalah in the formation of things from archetypal concepts to the World of Action.
The magician therefore needs to want the result more than they doubt or fear it. Then they must will it to happen with an appropriate level of investment for the scale of the result sought. Then they must not recall the line that has been thrown before the fish has a chance to bite, yet they must also provide a bait, and this is the creation of an environment where the opportunities of success can occur.