Trust is the foundation of strong relationships. It takes time to earn it and it can be destroyed by betrayal or neglect. Many people assume that trust is an automatic process that occurs without any or little effort on their part. That is an irrational assumption. Building and maintaining trust is an ongoing procedure that requires work and consistant effort. The saying "Fool me once, shame on you. Fool me twice, shame on me," was created by someone who knew that he or she had to watch out for those who he could be fooled into trusting and take note, so that the next time, he or she would not trust them, as they didn't deserve it.
Trust is a two way street. It is based on receprocity of communication, respect, and dependability. A pet, who loves you and trusts you will lay at your feet upside down and sleep, knowing that you would not hurt him or her and that you offer protection and companionship. People do the same thing, only with different signals, such as expressions of love, caring, kindness, affection, and intimacy.
Dysfuntional relationships lack trust. Suspicion, anger, criticism, and blame often dominate conversations. Effective couples or family counseling can offer tools and strategies to rebuild trust and acceptance of partners and family members. It takes time and efffort on the part of each person involved. But it certainly can be worth it as most humans want to be trusted.