This lecture discusses the transmission probability of protons through a potential barrier. Starting with a jet of protons with a kinetic energy of 5 electron volts hitting a barrier of 6 electron volts and 0.7 nanometers width, the instructor explains the relevance of the barrier and calculates the extremely low transmission probability. By considering the number of protons per second and the transmission probability, it is concluded that it would take an incredibly long time for a single proton to overcome the barrier, making it practically impossible.