Self isolation means literally self isolating. It does not mean going for walks or hanging out with friends, it does not mean your friends are any less infectious than perfect strangers, nor does it mean that you yourself are not an asymptomatic carrier of the coronavirus infecting everybody you come in contact with. The virus itself is not as dangerous as the people who spread the virus. We enable the virus. Without us exhaling it could not spread. Without us inhaling it could not spread. Every single breathing person you see including the person staring back at you in the mirror is potentially infected with the coronavirus, and the numbers of those of us who are infected is increasing at an exponential rate every day. The vast majority of people are infected by those in their family, and by their friends. Though you can be infected by a stranger you are far likelier to be infected by those you know very well.
Remember, the pandemic is not considered controlled until there are absolutely no new cases for fourteen days in a row. Because one infection very quickly becomes hundreds of new infections. That is how this becomes out of control so fast. That is why this is a pandemic. That is why everyone keeps telling you to please stay home.