Do humans really live in anguish because they’re ‘condemned to be free’? This was a view put forward by the existentialist philosopher Jean-Paul Sartre.

Do we all metaphorically wear a series of different masks to present ourselves to the world in the best light possible? The sociologist Erving Goffman thought so.

Is it possible to know oneself? And what good does it do?

What can we know for certain? Can we trust what our senses are telling us? Can we even trust absolute truths, such as those of mathematics? What if our brains are being manipulated to make basic mathematical errors?