5D3 shutter jammed

Aperture controls the throughput of light per unit time, while shutter controls the time allowed for light to pass. If you want the subject of the photo to see the hierarchy, you need enough exposure. For an inappropriate example, for example, if you connect a tap to a river and want to take out a basin of water, the tap (aperture) will be opened very wide and the time (shutter) for filling water will be very short; If you turn down a pot of water, it will take a long time to fill it. If the water flow in the river itself is very small (the light is insufficient at night), it is useless to turn on the faucet (aperture) again, so you can only connect it slowly (the blinds are opened for a longer time, which is what you call "stuck"). In this case, we can only use lamps to fill the light. If we don't do this, we can only improve the sensitivity of the original, but this will damage the quality of the photo.