To reach, experience and maintain a state of contentment or fulfillment you have to first realize what true freedom is and then learn how to use it so that it strengthens you and also helps you to achieve the full potential of your individual self. Freedom is the key to contentment. You also need to check what brings you close to the state of fulfillment and what takes you away from it. Fears of different kinds are one of the main obstacles in experiencing contentment. Any weakness, inability to apply any virtue or spiritual power required in any situation, lack of focus, inner instability, etc. will cause a leakage of the energy of positivity that is required to feel content. Free yourself of any personality trait that hinders your progress and does not allow your inner being to manifest itself and express itself with all its potential. To live in contentment, you should be in charge of your inner mental and emotional world. If not, you will only be able to experience temporary periods of fulfillment.
To achieve fulfillment you not only have to have inner control, but you also need to check whether there is any door open to allow any weakness to enter the room of your personality. Because if you strengthen yourself on the one hand and on the other you are weakened, you will never reach the desired state of inner power. E.g. you keep a bucket of water under a tap of water. If it has even a single crack, however much water you pour into the bucket, it will never get filled completely. In the same way, this can happen to you. Because of this, you need to check, which cracks are present in your personality through which there are leaks of energy, because of which your efforts to become content do not give you the results you hope for.