Scientists, politicians and psychologists say many Germans, including some in the government, made a fatal error of judgment after Germany emerged comparatively unscathed last summer: They thought they were safe.

This assumption, combined with the government’s imposition of a moderate lockdown in November that left all shops, offices and factories open, meant Germans didn’t cut down on social contacts nearly enough as the virus began spreading again rapidly through the country, scientists say.

Uwe Liebert, a virologist at Leipzig University, said Germany’s success in the spring “led to a certain carefreeness in the population.”

The relatively low level of infections recorded in the spring also meant many Germans underestimated how easily they could get infected this autumn.