> Once you have work deeply embedded in your interests and social life, it does not take a huge mental leap to "work is what defines me as an individual".

No, you are confusing cause and effect around emotional attachment and passion/effort.

People are equally likely to attach their sense of self-worth to aspects that require zero effort: nationality, favorite sport team, family name...

Putting a lot of effort into something is not the cause for attachment, but sometimes it can be the effect.