The difficulty bar is just an approximation based on a "normal" player's skill and the strength of your bears. It is possible in some cases to win even when the difficulty says "Impossible" if it was just barely impossible and if the player does much, much better than expected. So if you have nothing else to use your honey on, go ahead and give those "Unprepared" or "Almost Ready" matches a try if you haven't already.
In Story Mode, very good players will have a lot of "Unprepared" or "Almost Ready" matches because they have been "punching above their weight" and have already beaten missions that "normal" players haven't yet beaten.
Some of the other game modes (Daily Events, School, and non-tournament Special Events) have dynamic score-setting based on the game's perception of the player's skill. This makes the score target higher or lower so that we can use the same board for everyone without the strong players getting bored or weak players getting frustrated. If the game currently thinks that you're quite skilled, it will set the target higher accordingly. You should try anyway--if you win, great! And if you lose, this will help the game to tweak the skill perception (and thus the target scores) down over a number of days when it sees that you're not doing so well.
- Note that we don't use dynamic scoring in Story Mode, except for very early in the story to make the early missions a little less trivial for good players. If you're stuck in Story Mode, that's probably on you and/or your bears, not because of dynamic scoring. This page has some tips for folks who are stuck in Story Mode.
- Changes in dynamic scoring's estimation of your strength won't kick in immediately--it will take quite a few matches to move the needle significantly.
- For events that use dynamic scoring, once the score target is set for a particular event, that target is locked in for the day. So there's no point in checking repeatedly on the same day to see if it's gotten easier/harder.