For me, the tell-tale sign that I need to make a big change is because I've never liked any job I've ever had which involves being sat behind a desk. Although my employer is _challenging_, I've felt like that about five or so different employers and even working for myself.
On your first comment about not looking for your job to fulfil your life. I agree and disagree. I think that's fundamentally right and you need more in your life than your job and, honestly, right now I get a lot of my identity from my job and money and all that. Which I'm not proud of.
But the 'no' part is that I work hard and I always have done. 40 hours minimum and usually more like 50. And I work in the best part of the day when it's sunny and light. To squander all that time through my working life just seems horrendous. It's not like a couple of hours a day, it's the best hours in the best days in the best years of my life being spent switching pixels off and on in a grid using little buttons.