Struggle has a natural place in our life, but the fight or flight syndrome is often false struggle. There are times for that but we can have that reaction in areas of our life where it's not successful. Areas that concern existential issues or qualities of life - like meaning or purpose or love. These things actually come to us more as we let go of struggling to achieve them.
Most of us make an effort to do and be the best we can be, which leads to a distinction we need to make between the notion of struggle and the notion of effort.
The capacity to become aware of the givens of our existence - such as change - and to actually welcome those as just part of our human experience releases the struggle.
People around us change and circumstances change. We can often find ourselves struggling against those things.