 Space debris is a big problem, which is ironic because a lot of the debris flying around Earth at thousands of miles an hour are teeny tiny bolts and flicks of paint from old decommissioned spacecraft and satellites. Some examples, though, are full satellites which have run out of propellant and are dead weight orbiting Earth. Two examples are a spent Soviet Cosmos 3M upper stage and a parastate a relay satellite. According to Leo Labs, these two objects passed each other travelling in perpendicular directions at a distance of six metres. What you're looking at right now is a visualisation by Jonathan McDowell of the actual size and distance of the satellites to scale. A very bad coincidence of two derelict large objects in the same place at the same time could be a catastrophic pain to work around as one collision can create thousands of pieces of debris which, can all themselves, cause more collisions, creating more debris, causing more collisions, creating more debris, and I think you get the point.