Mick never seems to be satisfied with his achievements, although he is not depressed. while he does celebrate those achievements, they become normal after some time, and he moves on to the next big thing. this is best explained in terms of:

The answer is Adaption-level Phenomenon

Explanation: Adaption-level phenomenon is  a tendency which people have to adapt fast to a new situation until the situation becomes the norm. They get used to such situation such that it is no longer big deal to them anymore and another new experience is needed. If a new situation seems better than the current state the person feels better but only for a little while, if the situation however feels like a step backward, the person becomes sad and frustrated.

a. life is life.

because life is not always nice.

and life is not always fun and cute.

the trait of personality falls in the middle of the diagram because personality is a mixture of ones nature and environment.