Swedes have been asked to keep their distance in public, refrain from non-essential travel, and work from home when possible. Gatherings of more than 50 people are also banned. People age 70 and over are advised to stay away from others as much as possible. -From Medpage Today
There, it essentially says that they encouraged social distancing, less non-essential travel, and to work from home if able to. They also banned gatherings of 50 people. By essentially cooperating with citizens, they were able to lower case count. Now look at what has happened to Barcelona during the pandemic.
BARCELONA (Reuters) - Protesters who deny the existence of COVID-19 and object to restrictions to curb the pandemic's spread clashed with police in Barcelona on Friday. -U.S.News and Reuters (Article from 10/30/2020)
Restrictions were enforced hard, and people reacted to these restrictions. Sweden cooperated with citizens, while Spain had to enforce restrictions to try and control the spread of COVID 19.
See the picture above? See how, though people are wearing masks, 2 metres of distance between people doesn't seem to be visible anywhere? Masks do more when paired up with social distancing.
Remember when COVID had just appeared in Wuhan, China and became widespread? And how lockdowns and such happened later? And how easily COVID was able to spread globally? The virus can be brought to other countries, including countries like Japan. Hospitals and such weren't ready for this virus, so it should have been hard to treat. COVID can be asymptomatic, so you may not even know if you have it. This means that it could spread wihout the person who first had it in that area even knowing. I don't think that you would know you have an asymptomatic virus that was relatively new unless you got tested.