Dharmakirti was a really smart guy who lived a long, long time ago in a place called India. He was very interested in understanding how we know things and how we make judgments about the world around us.
He talked a lot about something called "valid cognition," which means when we understand something correctly. Like if we see a ball and we say "that's a ball," our cognition is valid because we're right! But if we see something that looks like a ball but it's actually a rock, our cognition is not valid because we're wrong.
Dharmakirti studied different ways that we can know things, like through our senses (like seeing or hearing something) or through logical reasoning (like when we figure out that 2+2=4).
He also talked about how our emotions and beliefs can sometimes get in the way of our valid cognition. For example, if we really want something to be true, we might convince ourselves it is even if there isn't enough evidence to support it.
Overall, Dharmakirti's ideas were really important in helping people understand how we make sense of the world around us and how we can try to avoid being tricked by our own biases and emotions.