Watch what you say and be especially careful not to say too much.
When Mercury squares Jupiter, our thoughts and words can go too far, we may push beyond our normal and reasonable thought boundaries into an extreme position. We may end up having said too much as enthusiasm got the better of us.
With Mercury in Sagittarius we are passionate about truth. But if we go too far, because something is pushing us, like the square aspect, we could slip into dogmatism.
Jupiter in Pisces is a reminder to consider that there are many realities, not just our own. But with Jupiter Squaring Mercury we could go beyond what we know and end up confusing our facts with our wishes or fears. We may go beyond reason into fantasy.
Mercury squaring Jupiter requires us to try and reconcile two approaches in our way of thinking. Mercury is "speaking" from the space of Sagittarius, that there is a "truth", but Jupiter is "shaping" that voice from the position of Pisces, that there are many "realities" to consider.
What we need at this time is to listen to Jupiter and bring more compassion into our thinking and communicating. We might be "right" given our point of view, given our reality, but we have to consider that there is more than one "reality".
If we really want to communicate, we have to try and understand where another person is coming from. We don't have to agree with each other, but we need to understand one another.