Sometimes we have to give up everything that we think we know even when it seems counter intuitive to do so. We have been conditioned to accept many things as fact that are in no way even related to such a concept. We seem to pursue happiness with a vengeance. A sort of "happiness or bust" attitude. We think that we are making genuine decisions in this headlong pursuit, but what we are actually doing is simply going through the motions of agreeing to one illusion over another illusion.
The one decision we are actually able to make, at least on the symbolic level, is that of listening to our Spiritual voice rather than our egoic voice. The ego identity has the much louder voice and tends to override the more subtle and peaceful presence of the Spirit. The ego cries out with logic and reason, and provides us with numberless excuses and stories why we should do this or that. Where the Spirit simply gives us a gentle sense of "knowing", and if we aren't being present in the moment, it will be completely missed.
The ego (with our permission) will berate us with every derisive device it can muster up to get its way. It will scold us if we don't "listen" to its convoluted ramblings. It will apply us with guilt or shame for falling "short" of some imaginary mark has been hidden from us until it is convenient to its case. The Spirit will simply give you a nudge in the most beneficial direction, a feeling that this or that will be in harmony with the greater good. So, if the arguments are verbal, and logical with an overtone of "demand" it is the ego that is in control (with our permission), and if the direction is a silent and subtle feeling, it is the Spirit.
When you have given over your control to the ego identity, you would do well to scrutinize the advice or direction you are being given. However, here again, lies another potential egoic trap in that every so often the ego will simply give an accurate instruction. Not through any "knowing" on the part of the ego identity, but just because as the old saying goes, "even the blind squirrel finds a nut every now and then." And when the ego does get a positive result, it will boast its success over and over with an over inflated sense of pride. The Spirit, on the other hand, simply guides you and that is all - no commentary, no boast, no pride. Even then the ego identity will often assert itself to take credit for the success of the Spirit.
So when we are seeming to make decisions like "maybe I'll get that new car, that will make me happy", or "I'm going to go for the more elaborate vacation, that will make me happy", or the bigger house or the new lover or whatever it is that seems to suit our fancy at that particular moment, we are simply diverting toward one illusion over another. In these cases there is some cause for a moment of passing happiness, but this will quickly fade because it is founded on an effect, or secondary cause, rather than a primary cause. We have placed some aspect of the illusion, an effect, in the seat of power and given it dominion over our happiness.
Since the effects are only reflections or projections of what is held in thought, they are temporary, and our Authentic Self is aware of their transitory nature. This Authentic knowing presents us with the instinctive feeling that they are short-lived, and that we will lose them at some point. This realization is where the happiness fades.