when u think any thing, one type of neurotransmitter is released in ur brain, then that neurotransmitter gets more and more released in ur brain via positive feedback loop in neurons.
for e,g. if u think , im not good enough, i cant reach my goal. then u triggered that neurotransmitter to release. and then u will spiral into thought that u cant reach ur goal because of positive feedback loop in ur brain
if u say to urself, im enough. i see my goal in front of me. then  ur thought triggered that type of neurotransmitter to release and u will then spiralled to reach ur goal because of positive feedback loop of neurotransmitters.
so, its upto u what u want to think in ur life.
this is only difference between successful people and failure people.
optimistic people sees opportunity in any adversity but pessimistic sees adversity in any opportunity.
everything in this cosmos happens for a good reason. it depends on ur perception how u perceive it