What is Gratitude?
Gratitude is not Excitement, which is rather the Fear of loss. Gratitude is not a purely mental, nor purely emotional state. One may 'feel grateful', yet behave ungratefully towards others and the Divine Principle. One can also say 'thank you' while not feeling grateful deep in one's bones. Behavior, as I hinted at, is a factor. Actions, not acting. However, actions taken with a poor attitude are of little value (or positive effect).
Gratitude is a state of Being, the state of Being Alive, in fact. Ingratitude, opinions and pickiness all stem from Excitement, again, the Fear of losing that which (or whom) we are attached to. This is the result of Self-Focus, also known as Selfishness, Service-to-Self, etc. We are afraid to lose what we 'have', which comes of the belief (false assumption) that we 'have' anything at all!
Our egos grab, wrestle and attach to everything & everyone in sight, in a desperate attempt to 'survive'. No ego has yet survived this mortal Life without complete surrender to Divine Grace, despite our hopes & flailing, we shall not be exceptions. How does one Become Grateful (again, as this is our 'natural state', one we have 'fallen' from at birth)? This is the purpose behind 'spiritual exercises', whether the practicer is aware of this or not, the process still functions (in Truth, excessive Awareness is often the primary hinderance to forward progress).
Gratitude comes about through the habit of placing the focus of one's life squarely outside oneself, on 'Higher things'. In the beginning, what these 'Higher things' look like in the mind's eye is not entirely relevant. It is enough to have a belief in a Higher power. The 'God' one believes in will be tainted heavily by one's own inner discord anyway, but this is of little consequence to the procedures of Growth. Part of this process is learning just what God (the Divine) is actually like, away from our own 'knowledge' on the subject. Merely coming to 'know', in a full-body manner, that we are not in fact the center of the Universe is difficult enough for the ego, and this represents the first phase of any program of spiritual development into the Mystical and Gratitude-filled Life, or simply 'Life', for short.
Taking our eyes off of our own egos (and off satisfying other egos in the world), placing them up to the horizon, on Beauty, the Divine, 'Higher things' uplifts our own selves. Fixing ourselves, punishing ourselves, improving our self-esteem... the common factor here (point of focus) is that of 'ourself', meaning our ego. Refocusing our whole life and habitual egoically-centered behaviors & activities will not occur overnight. This requires practice, as with any other learned skill. The more we practice 'lifting our gaze', the less of a struggle it becomes, the more natural it becomes in response to stressful situations. But, at first, do not be surprised to find it uncomfortable, perhaps frustrating, certainly difficult. Giving up on the process is easy, however sticking with it is rewarding, again, as with any skill we work towards mastering.
Mysticism is both hard work and a priceless (and impossible) Gift. We are saved by Faith, manifested through Works, to borrow a theological phrase of much debate. Both the Faith and the Works are Divine Gifts. We (our egos) have insufficient Faith to proceed, even in the midst of miraculous circumstances & conditions. Our Works are not enough on their own to 'save' (Grow/perfect) us either. Prayer works not (exclusively) in some magical, supernatural fashion, the vast majority of its effectiveness comes of all the time spent away from the selfishness of our egos. This is (part of, especially early on) why meditation 'works' as well. Anything we can become absorbed in can become an act of worship, if we are intentional about it. The danger as we settle in becomes thinking of what great worshipers we are, so much more grateful than all those other sad saps! Shut it. Be grateful to feel Grateful. If we think we are indeed so great, than we must make doubly sure to credit the Divine Principle in every breath for sharing the Divine Greatness with us.