The only way to be safe is to stay at home and not meet a single other person ever. Everything else is a matter of managing risk.
Wearing a mask does not guarantee you won't catch COVID-19 but, if everyone does it, it reduces the risk because those who have it trap a lot of the virus they expel in the mask.
Staying 2 m apart does not guarantee you won't catch the virus but the further you are away from other people the lower the risk. If you want to have a rule you need to specify a distance that defines when you are/aren't breaking the rule.
Having 6 at a table does not guarantee you won't catch COVID-19. Sitting together at a table automatically tends to put people closer together. You can't really wear a mask when you are eating and drinking and you are all tending to touch the same things so the risk is higher in that situation. The more people you mingle closely with the higher the risk. Again if you want to have a rule you need to specify a number that defines when you are/aren't breaking the rule.
Whatever you do the risk is higher where the infection rate is higher so you put in tightest restrictions where the infection rate is highest. For example you allow 6 to a table if the infection rate is low, drop that to 4 as the infection rate rises and then close tavernas etc altogether if it goes higher still.
The Greek prime minister did very well in the early phase of the virus where movement restrictions were about the only thing he could do to get the virus under control. He used them very well. He chose what to use very carefully, applied them effectively in a timely manner with the result that the peak was low and after the peak the infection rate fell rapidly. Copy book.
You can only use movement restrictions for a limited time, however, otherwise you collapse the economy. You have to use that time to put in place an effective test-trace-isolate system that can control the spread of the virus without movement restrictions. You use the movement restrictions until you have the daily infection rate down to a level that test-trace-isolate can deal with. You then slowly release the movement restrictions in stages checking at each stage that test-trace-isolate is coping. He tried to do that but the test-trace-isolate system was not effective. Which part(s) of that system failed I have no idea but it did fail. It's only purpose is to suppress the infection rate and eventually bring it to zero. If the infection rte is rising the system has failed.
Everybody wants to open up the economy. Many countries have done so very effectively or never really closed it down. They did so by having an effective test-trace-isolate system. It can work, those countries are living proof. Trump just wants to open up the economy full stop. He does not care how many people die as long as the Dow keeps going up. That's about the only thing he can claim to have done and that isn't really anything to do with him. As long as the Fed keeps printing trillions of dollars and using them to buy assets the Dow will go up.