The lack of a double coincidence of wants is a major reason why it is important to have a system of money.
Without money, we need to barter. But barter depends on a double coincidence of wants. If you and I are to barter, I must have what you want and I must want what you have. The same applies to you. If we do not meet this criterion, we lack a double coincidence of wants. If I have what you want, but you don't have what I want, we do not have a double coincidence of wants and we can't trade.
Because of this, it is much better to have a system of money. Then we do not need to have this double coincidence.