I would like to stress that very often famous people become reserved and angry with the world.

stress 在这里是动词，意思是"强调、着重指出"。这个词来源于古法语，本义是"施加压力"，后来引申为"强调重要观点"的意思。在句中表示说话者要特别指出某个观点的重要性。