What do we mean by ‘understand’?

What do we mean by ‘understand’? When I say, ‘I have understood something, it’s very clear,’ what does it mean? It is not an intellectual clarity, a mental clarity or an emotional, enthusiastic acceptance of something I don’t quite comprehend. So when we use that word, we mean total comprehension, seeing the thing immediately. And the immediacy of seeing is the immediacy of action. If I see something dangerous, there is immediate action. Out of understanding, there is not only psychological change inwardly but change in relationship with others.