This is the most important rule of safe ridind and driving. External, as well as internal conditions (expertise in riding, familiarity with road, concentration, fatigue, etc.) can vary widely. The brain does all the calculations unconsciously in background and finds out *your* limits for every conditions you meet. If you don't feel safe, you bet you aren't.

Accidents happen mostly when you take risks that exceed capabilities, or if you take the risks lightly (which leads to the same thing).