Can't believe I even need to point it out but I've seen so many threads where people say in one breath that they're self-isolating, and in the other they say that they're going for daily walks on quiet roads etc.
Self-isolating means staying indoors and not going outside, except in your own enclosed garden. No walks, no trips to the shop, nothing.
If you are avoiding contact with people but still going for walks then you are quarantining, not isolating.
It makes a difference because by misusing the phrase, the real meaning of it becomes vague and people who really should be self-isolation end up leaving the house because they think it is all right to do so.