I agree with the statement, we can’t believe 100% to someone even to our best friends. There is an old latinese philosophy that says “Homo Homini Lupus” which means a man is a wolf to another man. This philosophy is an image of human nature. The wolf as a creature is thought, in this example, to have qualities of being predatory and cruel.
It’s similar as the human nature, that human tend to ditch each other to fulfill their own needs and doesn’t even care what other people needs. This is why we can’t believe to other people 100%, even with our best friend because they are also human with this nature. They also need to fulfill their own needs and does not rule out the possibility for them to ditch us as their best friend to fulfill their needs.
It’s similar as the human nature, that human tend to ditch each other to fulfill their own needs and doesn’t even care what other people needs. This is why we can’t believe to other people 100%, even with our best friend because they are also human with this nature. They also need to fulfill their own needs and does not rule out the possibility for them to ditch us as their best friend to fulfill their needs.