Many people make vows when they are in dire straits, or undergoing extreme trials. This is an improper use of vows. By making a vow in such a situation, they are implying that God needs to be paid in order to answer prayers. Thus, they are misunderstanding and misrepresenting the love of God, and the care that He has for His people. Under no circumstances should you make a vow to God that you cannot or will not carry out.
Unfulfilled vows are detrimental to one s spiritual growth, as well as being unlawful.
So, vows to God should be very rarely made. We have burdens and infirmities enough pressing upon us. The dedication to a vow usually diminishes with time. It is best to fulfill a vow without delay. Often, an unfulfilled vow is yet another instance of our loose lips getting us into trouble.