For the less experienced, or for the emotionally unintelligent (or for those who have never experience mental illness), happiness is a thing to be had if only you simply made up your mind to have it.
Perhaps it is easy to make the decision to be happy, but like making the decision to take out the trash, it's the follow through that matters; then you forget and end up stinking like rotten eggs for a while before you finally get around to dumping the garbage.
"In the case of bipolar disorder, grandiose delusions are considered “mood-congruent delusions” in that they manifest from the manic (or hypomanic) state. During manic or hypomanic phases, it is believed that brain activity changes, brain waves speed up, and neurotransmitter concentrations change, particularly levels of dopamine." -Grandiosity in Bipolar Disorder: verywell.com