My camera, in common with most other SLRs, has a built-in light meter. It can be set to take readings from just the centre of the scene (spot), mostly around the centre (centre-weighted) or from the whole scene (multi-segment).
Last week, when shooting at a school play on 1916, I set metering to spot. I find this best in such situations, as then the exposure will be taken from the face of the subject without being unduly influenced by the background, which is generally much darker.
Two days later I was at the St. Patrick's day parade in Carlow town, and took a few dozen shots. When I looked at them at home, many were over-exposed, as I had forgotten to set metering back to centre-weighted or multi-segment. When the spot that was metered from was relatively dark compared to the rest of the scene the brighter spots were over-exposed, and I didn't check the histogram on the camera's view screen, as I should have, after any of the shots.
In the shot of the band, metering would have been from the dark banner, leaving areas such as the van at the back and the white coat on the right clipped.