Almost everywhere, you cannot feel 100% safe, because people are only people and something may always happen. Still, some places are considered to be more dangerous than the others.
While visiting big cities in Brazil you should stay very careful, e.g., even Brazilians warn foreigners about Rio de Janeiro. I don’t have any bad experience, but I know people who weren’t so lucky.
Thanks for this information. Before I plan to go abroad I inform myself about the safety. E.g. I’ve heard about some rumours that the security situation in Tanzania is getting worse. Thus, I decided to go to another place this year.