Nick wants to be seen as a hard-working, self-made man who took a path few others have the intellect and work ethic required to pursue, winding up as an elite among society. It's why he worked at banks for his early jobs and picked "lawyer" as his pretend profession. Lawyer is a position that stereotypically was considered an intelligent and "elite" job. The problem for Nick is that by the time he got into it people were already waking up to the fact that lawyers were retards and not just scumbags.
It boils down to Nick being a trust fund baby who never had to work hard a day in his life, stumbling his way into a low-effort and easy job that catered to his narcissism and desire for approval. Even at his HEAVIEST workload, he still never really needed to do much show prep. He reads documents and reacts to them as a "lawyer" that doesn't ever have to worry about being proven right or wrong. The maximum show prep he ever had to do was "Let's google current events and see what I should talk about today". Very noticeable when it is missing, but hardly earth-shattering work when it's there. So his "work" amounts to simply spending time sitting in front of a screen and talking.
His entire life is the antithesis of what he wants to be perceived as. That must eat at him on the deepest level he can feel, especially when other people bring it up. It's why he exaggerates how hard his life is and how hard his show is while simultaneously wanting to look like he's got it on easy street. Because he wants people to think his life is some massive difficulty, but he's handling it so fucking well we should be jealous.
The funny thing is that the one thing he actually can accomplish that would be impressive and worthy of respect is raising and caring for his wife and 5 kids. And he fucking HATES it. We have all seen how much he despises his family and kids. The reason? It's the one thing that has ever been in his life that actually requires work, and he is likely failing at it. Sure his kids aren't going to die, probably. That fact is something he probably tries his best to hide behind. But kids not dying is the default position. I'm sure he sees every day the damage his and Kayla's poor parenting has done to their kids and resents the fact that it would take even more work to fix/prevent it. Don't get me wrong, by the way. It's not that he cares about the well-being of his children. He just cares about how their success/failure represents him as a father and his success.