Twenty years ago, when Andrew and I were still in college, our psychology professor taught us a lesson that we will never forget. She had to tell us that that was a vital question concerning our thoughts and world views. When she raised a glass of water over her head, everyone expected some kind of classical metaphor or a half-empty glass of water from her. She demanded from us: “What do you think, how much does this glass of water weigh?”

The students began to shout out options from a few grams to half a kilogram.

For a few seconds she listened to the answers with a benevolent smile and nodded her head, after which she replied:

“From my point of view it is not so important how much this glass weighs in grams. It all depends on how much I will keep it".

"If I keep it just a minute or two, it will seem pretty easy to me. If I hold it for an hour, my hand will start to hurt a little and I will feel tired. If I try to hold it all day, then most likely in a few hours my hand will go numb, it will be taken away, and I will drop the glass on the floor. In all these cases, the weight of the glass does not change, but the longer I hold it, the heavier it seems to me."