Why the dream arrive.?

I had a question why  the dream arrive ?
Not all the time but only particular time.
I was having soo many questios that ,

Why the dream arrive ?.

Why person have to dreem?.

At wht movemwnt the dream arrive?.

If all the dreams  are true?.

And soo many question .........

Do u know when a persam experience a dreem?
I will give you a answer according to science,
Person will dream at the three stages.

1.  When person is verry happy.
A person will dream about what he had done  or what  he would  have been done and what he had missed  that day.

2.when person is in the tension.
That is When person is the any of the trouble  he will be thinking about that solution  that solution  can be given by the dreem some times.

3. This is the dream  will arrive  for the people who wilm be sleeping  excess  sleep more then a person can sleep.
Thus drems  will give the experiences of  some new things in their  life's.
Yes some times we attend the situations  where we will be having a guilty that  before  also we had deal such a situation.
Yes u deal  but not  in real life but in dreem .

All the dreams have their own  reasons  and own principals. 
But all of them are the things which we do remember the things.