Perception. As an individual, there is no greater tool in your arsenal than perception. The Stoics spoke about it - "Our life is what our thoughts make it". The spiritual masters in the east have created centuries worth of practices based off of perception: Yoga, meditation. These are beliefs, ideas, foundations, fundamentals formed in the B.C times of human existence. Throughout even the earliest parts of civilization, philosophy, and education there has been this understanding that our reality and our perception of reality are intertwined so tightly they are indistinguishable from one another. They are one and the same.
The things we find sexual or attractive, a direct result of culture and shared perception; beauty standards. The objects of desirability result from what you've been told is desirable and whether you've allowed that perception to attach to your own personal perception - making your desire towards this thing a reality.
CBT, Cognitive Behavioral Therapy, the most extensively used and effective tool in psychology. This is a psychotherapeutic process that forces you to identify thought patterns, recognize them the negative ones as unwanted, and then dismantle and replace or overcome them. It uses exposure therapy, a form of rewriting trauma and impulse reactions through overloading them with positive or neutral perceptions on the same subject. A brute force reconfiguration of your perceptions that completely reshapes you reality. CBT calls upon you to look at that which hurts you and then reclaims its ability to do so. Its a tried and true formula. This is one of the most basic forms of psychotherpy but is undeniably one of its most effective.
A person who can achieve great things is one who believes that they can achieve great things. Self efficacy and your belief in how much you control and your propensity towards positive outcomes go hand in hand. The Locus of Control. A person who believes they are in control of their outcomes tends to also have high self esteem and self security. They are able to withstand negative life events with more resilience. All because of perception. The difference between "Things happen to me" and "I make things happen" is enough to make you a stronger person, measurably so.
This doesn't exactly mean you can just think your way into happiness and success. Concepts like that are also crafted in the mind and aren't even understood by those who spend their lifetime quantifying it. Contentment isn't a goal that is reached. Contentment doesn't result as a matter of simple accumulation. Contentment is a long never ending process of evaluation and reconstruction. Contentment is forever spontaneous and fleeting - you must always keep it in reconsideration. Unfortunately most people don't reshape their conception of contentment until those moments where they are at the end of their ropes.
Maybe there's a sense of shame that people feel in reaching towards contentment. The higher functions of our intellectual brain equate being fine with "good enough" as tantamount with just giving up on your passions and dreams. To be fine with what you have is to kowtow to a mediocre existence.
Stoicism and Buddhism answer this by asking you to "Just Exist". They get to that conclusion in very similar ways but their definitions of just existing are very different. Regardless there is this understanding that we are the masters of our own universe. That feeling and being are one. That experience is a matter of curation, not simple passive observation. But observation is the very thing that gets you to be able to curate your existence.