It is like waking up in the morning and seeing that it is raining. Someone might say it's going to be a good day, someone else might say it's going to be a bad day.
Your answer reflects your outlook.
The comparison is not exactly in its place. Liechtensteiner believes that the answer is found on what happened before so as to understand the present state of the glass. This is a nuanced way of looking at it, and it's more accurate, but I did say to him that both can be said actually, if one would not be specific in this.
The reason why your comparison is not in its place, is because your comparison is about judging the rain (at present) based on how one feels that the rain's effect will be (in the future). A farmer will see it as a good day, but a soccer-player who has a match will probably see it vice-versa.
With the glass, the state of it is already known (its past and present are already known). As for the rain, then one still has to see what will happen in the future to understand the state of affairs. Why would one judge the past and present of the glass with his feelings while the state of it is already known? As for the rain, then I can understand why one would judge the future with his feelings based on seeing the rain.
Edited 8/2/2020 16:35:39