It's a pity--we are sentinent enough to ask the question "why" but not smart enough to come up with the answer.
I'd like to expand a bit on this. There is a built-in glitch in our self-awareness and reasoning as to our motivations. Most of the time what we do has no cognitively determined intent. Children are being truthful when they answer "I don't know" to the parent's "Why did you do that?" The truth is that most of our decision-making process is not done in a way that we "see" it.
There is a bias for rapid decision-making and action, especially in times of stress, which has survival value. Animals who take too long to decide if a flicker in the night is a threat do not live to reproduce as much as faster reactors. This is why stress hormones activate a special memory retrieval system and memory base that resides in the limbic system rather than the cerebral cortex. On a more mundane level, we avoid overburdening our brain by the use of habit and even random behavior to avoid conscious thought in every decision.
But we still have that pesky curiosity which demands that every action must have a "reason". So we make stories up; stories about everything. Literature and folklore are full of "just-so" stories which give "reasons" for common observations. The story of Noah is, among other things, an explanation of rainbows; the story of Job is an explanation of why bad things can happen to a good man. All cultures are filled with these stories.
And we make up "just-so" stories about ourselves and why we do things. Redheads have a temper and the Irish drink to excess. So be careful with redheaded Irishmen in a bar! In truth we do what we do because that is what our non-cognitive decision-making processes determined we would do. When asked why we did that, we feel compelled to provide a logical reason, so we make up a "just-so" story. In this way the cause is created after the event to explain the reason for the event itself!
One last observation: some people seek to understand these processes and view what is happening in their own minds. They peel away the "just-so" stories and try to see what happens behind the curtain. They look for how people are interacting with each other, rather than how people SAY they are interacting with each other. Neuroscience has a large role to play, but so does millennia old contemplation and meditation.
Peace all.