Safety advice about neighborhoods is almost always either too panicked or too casual. The panicked version tells you not to leave your hotel after dark in any city in Latin America. The casual version tells you that 'anywhere is fine if you just pay attention'. Both are useless.
Our honest version: 99% of tourist crime is opportunistic theft — pickpocketing, bag-snatching, distraction scams. It happens disproportionately in crowded tourist areas during the day, not in 'sketchy' neighborhoods at night. The Las Ramblas, the Trevi Fountain, the metro between Gare du Nord and Châtelet. Not the dark alley your guidebook warned you about.
Real safety advice is almost boring: do not carry valuables you do not need, keep your phone in a front pocket, stay on busy streets at night, do not get into unmarked taxis, trust your gut if something feels off. That covers about 95% of cases.
The other 5% is neighborhood-specific. Before you go, ask a local where not to walk after dark. Every major city has two or three such blocks. The information is easy to get if you ask. And crucially, those blocks are almost never the ones travel-safety articles warn you about.