If they are doing their jobs properly: on-call should rarely wake someone up in the middle of the night. If it does, it's for an once in a blue moon issue that

If they are doing their jobs properly: on-call should rarely wake someone up in the middle of the night. If it does, it's for an once in a blue moon issue that wasn't predicted. This is fixed and never happens again. Then in a few months something else happens, and the cycle repeats. If they are handling it poorly: they will overwork the poor sap who gets assigned to oncall (in disfunctional companies, this is likely to be the junior-most members, who don't yet have a say on the matter). Things will be barely patched and people will quit.