In the United States, the last Monday in May is Memorial Day. It is a day meant to recognize those who died in service to their country. The tradition is to visit a cemetery and to lay a wreath, or tidy up a grave. If you have a fallen soldier in your family, you'd visit his grave, otherwise it's traditional just to visit the grave of any soldier, such as one from the Civil War or World War I - someone who probably has no relatives left, and whose grave has been left untended.
As poignant and sobering as all that is, Memorial Day is also considered to be the unofficial start of Summer. It's a holiday, so people have the day off from work, and the weather is usually bright, sunny and warm. It's a time for barbecues and picnics and weekend getaways. So even though we're temporarily saddened while visiting the cemetery, and deep in our hearts we know that someday we'll end up in that same place, at the moment the sun is shining, you can smell charcoal grills in the distance, and the beach or the open road is summoning you. No time to dwell on the brevity of life - pay your respects to the dead, but then get out of there, forget about it and enjoy life!
In this case, the shadows aren't dark and gloomy scary type; on a bright May day, the shadows that are cast are a place to get out of the hot sun and maybe spread out a blanket and have a picnic or read a book. The oblivion of the present - we are too caught up in our daily tasks and obligations to think of the past. We so busy every day that it makes us oblivious to the past. (For example, on average day, while rushing around, getting ready for work, commuting back and forth, working all day, coming home and taking care of household chores, etc., very few of us pause and think about things like World War II or the Black Plague or other very serious parts of history. We're obvlivious to everything except what we're doing at the moment.)