Actually, it's pretty simple. Deep inside the heart of every man is a secret wish to be trusted. How many times have men said to their wives, "If you would just trust me." Many men wonder why it seems so difficult for their wives to do something so seemingly simple. The answer stems from the physiological differences between the sexes.
It begins at birth when little boys are given a distinct physical advantage over little girls by having higher levels of testosterone. With testosterone comes the physical strength to both defend themselves from danger and/or run away from a threat. Most little girls don't have that ability. They don't have the strength to defend themselves physically in a fight when they feel threatened. If a boy trusts someone who in turn hurts him, he can always defend himself physically (or try to). Little girls don't have that physical option of power. Since a person can only trust from a position of strength, those same little girls will grow up into women who naturally have a more difficult time "trusting" when they feel vulnerable.
So men, when you ask the woman of your choice to simply "trust you," it's not that she can't, she's just more vulnerable than you. If you want her to trust you, she needs something that will help develop that trust. Perhaps even a tool or gesture that she can "count on," until that trust with you is established. Thankfully this tool already exists and is known to every woman. What cultivates trust in a woman is a man who consistently keeps his word. Making a promise is meaningless if there is no follow through.
A woman needs to see her man fulfill his promises because seeing is always more powerful than hearing. Allow me to illustrate. Imagine someone told you that I was the meanest person they had ever met. For months all you heard was how terribly I treated my family and friends. Then one day you met me and during the course of our meeting you begin to notice that I didn't seem to be as horrible as you were led to believe. I actually appeared to be rather pleasant. Would you change your entire opinion about me from one visit? Probably not! However, if you saw me respond consistently with kindness and humility over a period of weeks, your opinion of me would begin to change. A paradox has just been established. The kindness you have seen in me for the last few weeks does not match what you have heard about me. All the rumors of how mean I am begin to fade into darkness because of my consistent actions. Over time what you see will replace most if not all of your concerns about my character.
Men, with all the relationship advice I give, I must tell you that when the woman you love sees your words lining up with your actions, trust will naturally follow. When you don't keep your word it causes your wife/girlfriend to become fearful. From her perspective, she has entrusted you with her Heart and wants to trust you. She simply needs your help in giving you what you want.