Both of these two symptoms are the loss of concentration. Cross-eye is a situation that one eye is focusing on the object while the other one is straying away and doing its own thing. Lazy-eye is the situation that one eye is slower in focusing than the other.
There are two causes of the loss of concentration. The first one is stress. When we are stressed, the muscles around the eyes are tensed up and tend to be strained. Strained muscles can pull the eyeball away in any direction they like. Under this circumstances, it will only get things worse if we still try very hard to focus.
The other cause of strabismus is the imbalance between thoughts and feelings which are unconscious problems. Our left eye reflects our feelings. Our right eye represents our thoughts. When conflicts between thoughts and feelings occur, both eyes will refuse to work together.