What is the meaning when someone say "It went by really quick,I couldn't get the full picture?" What does full picture mean? Thanks everyone?

Like if a car passes you going fast - you may only see that it was a car, and it was red, but it was too fast for you to see anything more about it - like what model it was, or if it was a convertible, or who was driving, or the license plate.

the full picture means the total idea or a complete understanding. The thing happened so quickly that some (probably important) things were missed. You cannot have a complete understanding if you missed some important things. Otherwise, they would not be important.

I couldn't get a complete understanding.

Means wait: I moved too, so I made a mistake for catching the picture,
correctly.

I think this sentence means that time goes so quickly and I cannot recall all the things in detail. Maybe something is on the tip of my tounge. I cannot remember the whole thing.

In the short time he had it was not possible to realize the full enormity of the problem or situation

It means his recollection of the event was fragmentary. Before speech allows a person to remember something symbolically by words, his mind can only recall pictures. If there are gaps it the recall of picture(s) it can be said that one could only recall part of an event but failed to observe and remember all of the event. He was unable to get "the full picture (of the event) into his memory from his senses.

big picture
: the entire perspective on a situation or issue

https://www.merriam-webster.com/dictionary/big%20picture

http://www.wisegeek.com/what-does-the-big-picture-mean.htm

the big/bigger picture
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the most important facts about a situation and the effects of that situation on other things:

http://dictionary.cambridge.org/dictionary/english/big-bigger-picture

http://www.wordhippo.com/what-is/another-word-for/the_whole_picture.html

the whole picture

http://idioms.thefreedictionary.com/the+whole+picture

http://www.thesaurus.com/browse/the%20whole%20picture