The evolution of cards
Definitely losing to a weaker hand. Whenever I decide not to play one hand I have made a conscious decision to disregard it's potential and therefore I can not blame anything but myself.
However, whenever playing and losing to a weaker hand one has already anticipated a win (or almost anyway). You could argue to that the weaker hand isn't actually weaker since it won. As a medicine student I could see an analogy to evolution; there is no such thing as a weak or strong gene (gene expressions). However some individuals have more adapted gene (or gene expressions) to the environment than others. If one imagine that the mutual cards are the environment, and your hand is your "genes" there is truly nothing such as a strong/weak hand, just hands more or less adapted to its environment. Please share your thoughts regarding my (probably slightly weird) analogy.