Also -- regarding the question about needing energy and doing it without or with less caffeine (I just read the rest of the posts after the first handful to get caught up), I think sleep/rest and training are key, but it's mostly just about what works best for you as an individual.
I used to always lift in the evenings after work. It's just what I'd always done. My body likes to naturally wake up around 9 AM and could stay awake til about 1 AM -- a good 8 hours of sleep, but that particular schedule isn't very conducive to work/most things in life. So, obviously I had to wake earlier than that for work and try to get to sleep earlier than that. It never really mattered how much sleep I got, my body just kind of wanted to operate on that schedule.
Anyway, I've since started training first thing in the morning before work, which means waking up before 5 AM most days. And trust me when I say, my body does not want to get up then -- but I do it. And when I do, I feel SO much better and more productive the rest of the day. To be honest, I could do it without caffeine, too; I just don't want to. But training in the morning gives me a much better endorphin release and much more focus throughout the day. I'm just far more productive at work. And when it comes to just getting through the day vs. excelling, you're absolutely right that there's a difference.
I would evalutate diet, sleep, training, and micro-nutrients/multi-vitamin usage. Beyond that, it may be worth looking at nootropics, too. That's not a must, nor should that alone be the solution, but it certainly can be another tool to keep tucked away.
Additionally, I'll say that working manual labor was leagues easier than working a desk job or one that's mentally taxing. I worked 12's doing construction for 60 hour weeks back between years 1 and 2 of grad school and I was dead tired when I got home from physical exhaustion, but it was easy. Just the same as I can go out and push mow 2 acres and haul timber to burn and clean up my woodline and it's a cake walk vs. sitting in a stupid office and doing paperwork. So yeah, it's all about what you're used to and how it affects you, but for me personally, I need more caffeine to get my brain through the day vs. my body.