I don't know about you, but I'm constantly going back and forth between "Do I have enough?" vs "Am I being too conservative?" I'm mid-30s so I've probably got 30-40 working years left, barring medical/injury events. I get my 15% of gross saved every year between company match, 401k, and IRA contributions. I was luck that for the first 7 years of my career, I had an employer who matched my 6% with 10%, so I was putting away 16% of my pay starting in my early 20s.
That being said, I do wonder if it's too conservative, at times and if I should be doing more to enjoy life now. Like, not being so stingy when looking at new toys or trips for my wife and I, and our family.
Here's my advice. Retiring very comfortably is VERY simple. Invest as much as you can for as long as you can. It isn't EASY but the formula is simple.