Memories, as we all know, are the echoes of our past experiences. They can be joyful or sorrowful, and sometimes both at once. What makes memories so powerful that they can evoke a range of emotions from happiness to sadness? Let us delve into this complex question and explore what it is about memories that make them feel so bitterly sweet.

The first thing we need to understand is the concept of nostalgia. Nostalgia is a sentimental longing for the past, often accompanied by feelings of wistfulness or melancholy. When we reminisce about old times, it's not just about recalling events; it's also about evoking those emotions associated with those events. For instance, if you hear your favorite childhood song on the radio after many years, you might feel a wave of nostalgia wash over you. This feeling could stem from happy memories associated with that particular song.

But what happens when these happy memories turn sour? When something goes wrong in our lives or someone leaves us behind forever, those same cherished moments become tainted with pain and regret. The realization hits us hard: "Why did things have to change?" "What did I do wrong?" These questions echo through our minds like haunting melodies until they consume us entirely.

One such example comes from Fyodor Dostoevsky's novel "Crime and Punishment". In this book, there's a character named Raskolnikov who murders an old pawnbroker lady out of sheer desperation but later feels immense guilt for his actions. His journey towards redemption takes him down memory lane where he encounters her again in vivid dreams filled with bitter sweetness – remembering how she used to help him despite knowing his troubled background only adds salt to his wounds.

Another poignant scene comes from Shakespeare’s play “Hamlet”. Hamlet laments over Yorick’s skull during Ophelia’s funeral saying:

"Alas poor Yorick! I knew him well."

This line encapsulates the bittersweet nature of human relationships – while Hamlet holds onto their shared history fondly (the good times), he cannot escape the fact that death has torn them apart (the bad times).

These examples show how even beautiful memories can become painful when circumstances change irreversibly. We then ask ourselves why does time move faster when we're drowning in these emotions? Why does each passing day remind us more intensely than before?

To answer these questions fully would require delving deeper into psychology but one thing stands clear - human beings are creatures built upon contradictions - capable of great love as well as deep suffering; strong enough to conquer challenges yet vulnerable enough for heartbreaks.

In conclusion, what makes memories bitter-sweet lies not only in their ability to evoke joyous reminiscences but also their capacity for stirring up regretful feelings born out bitterness & loss – reminding us constantly that life itself contains both beauty & ugliness intertwined like two strands within an intricate tapestry called existence which never ceases fascinating humanity since its dawn on earth till date!