In the last few episodes (check here), we slowly built up a comforting picture and learnt how qubits are prone to errors and how we can correct them etc. The conclusion is that:

Yes, qubits are fragile. Yes, they suffer from errors. Yes, we have clever ways to detect and correct those errors. It almost feels like we have solved the problem! But there is a catch.

To understand this, let us go back to something simple.