No doubt you have heard this said quite a few times. I would speculate that you will have heard it most in the context of some pseudo-psychologist advising people how to be a better person. At least, when I think back to those occasions I have heard this piece of advice it has been on some self help program on television or in a book in which the author claims to have a special life lesson to impart to others.
I also recall having heard it from some men and a few women, who have presented themselves as preachers in churches, but have had more to say about some crude and amateurish mix of home brewed psychology than the Word of God. There was also the worship leader who wanted people to let themselves go emotionally in their worship behaviour "Trust yourself" was his exhortation.
Then there was the time only recently, when I asked Sonja to hold something in place so I could drill some pilot holes for screws. The thing was, she had to be positioned in such a way that she couldn't see what she was holding or what I was doing. So, quite naturally she was somewhat apprehensive. My response, with the electric drill whining in our ears was, "Trust me."
There are two people I have an instant distrust for, and who cause me to question everything they say - these are people who I have seldom or never met before, and who I neither knew in any other way or who know me, but who say "Trust yourself" and "Trust me".
Trust is something that can never or at least should never be given without very careful consideration, and some very clear evidence that the one in whom you are placing your trust won't let you down.
We all know this to be true. Life teaches us this lesson all the time, sometimes at great cost and pain. The man who cheats on his wife should never wonder that it will take many years before his wife will ever trust him fully again. The daughter who promises to abide by the rules her parents set down as acceptable behaviour, but finds delight in flaunting her rebellion need not be surprised at their efforts to impose even stricter controls. Those who are caught in telling lies have to work hard to rebuild trust in the truth of what they say. We can obviously go on with many other examples, but we know this is true - trust must be earned, and when it's broken it takes a lot of time and careful effort to restore.
That's the thing about trust. It is a fragile quality which takes considerable quantities of commitment, loyalty, honour and honesty to form and shape it into something which others will respect and find they can rely on, but it is broken and shattered in an instant.
So anyone who breezes into your life and wants your trust is asking you to give them something that needs to be handled with great care and something that is very precious. You don't just give this to anyone. We need to be sure of what we are doing.
I wonder though, about the other form of trust, the one that isn't given to others but which we are supposed to invest in ourselves. I think sometimes this is confused in our minds with self-worth or self-esteem. Popular opinion seems to be that you can't trust yourself unless you value yourself. It seems however, when we listen to what God reveals concerning human nature, it's not only other people who are to be 'suspicious' about until there is some tangible proof to their reliability, but we are to be equally careful about ourselves.
How many times has it happened that you were quite confident about being able to safely enter a situation where you knew there would be a temptation to sin before God? You were so sure of your ability to stand above it and resist, only to find your confidence in yourself was not as it should have been.
People are simply not trustworthy! Of course the Bible tells us why. "For all have sinned and fallen short of the glory of God (Rom 3:23).
That's what makes God the only secure One to trust. He has not sinned, and one aspect of His glory is that He can be trusted utterly. He has never in eternity past said or done anything which has betrayed His trustworthiness. His promises for good and bad are fixed and absolutely sure. They always have been, and they always will be.
Our history with God as a human race extends back a long way, and the only ones to break trust in that history have been people - every single one of us.
So anyone who says to you "Trust yourself"; you know doesn't know himself and certainly doesn't know you, and probably doesn't know God either. When it comes to trusting others we better have a long relationship with them before we invest that precious commodity.
The Psalmist wrote, "Some trust in chariots and some in horses, but we trust in the name of the Lord our God" (Ps 20:7). Only God is a truly secure refuge (Ps 62:8), or as the Lord Jesus said, "Do not let your hearts be troubled. Trust in God, trust also in Me." (John 14:1)

Albert Esselbrugge