The rise of nuclear proliferation is what ultimately paved the way for the Cold War. Several nations suddenly found themselves with the unprecedented power to completely annihilate whole cities and countries with a single bomb. This thrusted the world into a new nuclear age where these weapons turned into bargaining chips. The bombs were only used twice against Japan in WWII, and that seemed to be enough to reassure all nuclear powers not only of their immense power, but also their immense role in serving as deterrents against other countries. Unfortunately, this sentiment has persisted to this day.
The reason why these weapons have not been used since is because nuclear powers are well aware of the risk of a nuclear holocaust should any single country resort to using them. Therefore, nuclear bombs serve only to deter others, rather than threaten with actual usage. These weapons are seen as a last resort, with the main implication being that their use would completely devastate and transform the world as we know it.
Despite serving as deterrents for the time being, their very existence poses a continuous threat to the world. Moreover, rising tensions between nuclear powers means that no one will willingly give up these weapons when others still possess them. The most severe danger, however, is that these nuclear weapons can fall into the hands of rogue actors, or even hostile countries such as North Korea.
A nuclear mishap can only be truly averted if all nuclear powers decided to get rid of their weapons. Until them, there is no guarantee that the world is safe from a nuclear holocaust. Furthermore, given the rising tensions between the two most powerful countries—the US and Russia—it is highly unlikely that we will witness any kind of disarmament in the near future.