Famous sayings about understanding are 2 pieces of understanding between people. Not people understand things.

Fully understand, which is the definition of friendship in French. —— Emerson

understands everything and tolerates everything. —— Roman Roland

The most outstanding things are often the most difficult to understand. —— Edison

Understanding is undoubtedly the soil for cultivating all the fruits of friendship. —— Wilson

I can't believe what I can't understand. ——— Sartre