Relating these terms to types of human thought, we might say that quicksilver indicates a temperament that is mercurial and elusive; jellyfish pertains to an absence of stamina; and double-mindedness points to unsettled, vacillating, deceitful thinking.
As long as a trial is considered a trial, it will seem to be one! Conversely, when trials and adversities are viewed as opportunities to awaken us to life in God and to forward our spiritual birth, they have inestimable value.