People can be roughly fungible, but relationships aren’t fungible.
‘If I didn’t have you, somebody else would do’ (thanks Tim Minchin!) But once I have you, and spend 10 years building a relationship, someone else will not do.
Houses are roughly fungible, but once I relate to a place as home it is no longer fungible.
Many jobs/roles are worthwhile before you take one, but once you have one, that’s the one you want to build and keep.
Maybe ‘jobs for life’ used to be this too. I never lived through that to be able to tell.