which stage of life is associated with feeling a sense of accomplishment and regretting missed opportunity?

Generativity and Stagnation /  also known as midlife-crisis

Explanation:

Typically, this stage of life occurred between the age of 45-60. People who live in high competitive area (big cities) tend to experience this stage sooner compared to the people who live a sedentary life style in rural area. During this time period, most people already old enough to be able to evaluate themselves.

They'll reflect on their experience and determine whether the things they did are suitable to their full potential.

If the answer is yes, then they will a sense of accomplishment.

If the answer is no, then they will most likely feel regret.

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