Everybody wants to be happy. To experience happiness continuously we have to make a choice to be truly fearless - in simple words peaceful. To be peaceful you have to make a choice not to be afraid of happiness or sorrow. To be brave you need knowledge - thorough and mature understanding of the perceivable aspects of happiness and sorrow.
Given that one has bounded rationality he will make choices that maximize the probability of his eternity. According to Brahma Kumaris we are eternal in abstract sense like the way a theorem in math is true in abstract sense. For a theorem to be "useful" it has to be "applied". Similarly we (souls) need bodies. Either in soul conscience (theory) or body conscience (practice) the tough part is in the finer details. We are not yet evolved to skip lot of details in the process of analysis.
Let's dig some details of happiness and sorrow that will help in finding peace. Happiness has been researched a lot and you don't have to be attached to your superficial analysis of happiness. No matter how detached you are from your fleeting views on happiness there is still a need for detachment from your perception of sorrow to complete the requirements for peace. In any optimization theory we have the techniques of zig-zagging or changing momentum to avoid getting stuck in local optima. Experiencing sorrow is a similar technique (designed by Nature) that drives us towards global optima in life and avoid getting stuck in local basins. You can also look at the section on adaptive benefits of depression here. There is no absolute detachment from anything it's just elevating yourselves to higher layers of perception and getting detached from lower layers. BEWARE, the act of being in higher layers of perception is in no way superior if you are not aware of the layers you have passed through to get there. Just to be in the layer where you are without effort to elevate is probably being lazy.