I was thinking about this and a comparison came to me. I always like to look at things like this from the parent/child relationship perspective.
What do I do when my kids ask me for something? I have this picture in my head of pouring Goldfish into their hands. We show them how to hold their hands just so, but if they are in a hurry it's going to spill. They aren't going to get all that they could have gotten if thy had taken time to "prepare" to receive the Goldfish. (i.e. get a cup, or hold their hands closer together, etc.). They will still get some, but will probably get hungry sooner.
Same with us and getting the things from the Lord that we ask of Him. He is constantly pouring His grace and mercy out on us, but if we never take the time to properly receive it...if we just grab some on the go...we are never going to quite have enough to satisfy. But if we take the time to hold out our hands and arrange them to best carry what He is giving, AND to keep coming back for more...we will have all that we need and then some.
The box of Goldfish (Grace) is going to still be sitting there waiting for the next pair of outstretched hands.