I estimate that I made between 2B and 3B isk in profit during my time as a station trader. This consisted entirely of placing buy orders and sell orders, all without ever undocking from Jita. Station trading is great for making isk, since it scales fairly well with the amount of isk invested. Although profit scales nicely with the number of active orders that are placed, beyond a certain point "fun" quickly goes down (at least for me).
Dealing with burnout is probably the biggest problem that I face with any of my business endeavors. With station trading this can be a big problem. Thing about it: what happens if you burn out while you have billions of items listed for sale or purchase? Cancelling buy orders is simple enough, you forfeit the brokers fees you put up, but that's a sunk cost anyway. The items you have listed for sale are a bigger problem. The difference between actively managing items for sale and liquidating everything to the highest buy order was well over 5% for the items I traded, meaning the average station trader would be losing hundreds of millions of isk. Leaving the items sitting in your hangar is also rather pointless, and potentially unfeasible if you need the liquid isk on hand.
I wrote about how I'm on track to make 1.5B/month from my PI factory planets in an earlier post, but this number assumes that my planets continuously run 24/7. For this to be true, I have to consistently load and unload customs offices every two days on all my planets on both my PI alts. Realistically, this isn't happening because it's incredibly tedious work. Fortunately, if I fall behind I may not maximize my profit, but I'm not really losing anything. The P2 goods will still be sitting in my launchpads if I ignore my planets for a week. The only problem is, if I decide today that I don't want to do PI anymore, then the input P1 commodities I bought are now worthless. They would have to be liquidated, probably at a loss.
The risk of burnout is the main reason I haven't looked into doing research, or manufacturing, or drug production, or anything else that requires a POS. A POS requires fuel every month (a fixed expense). Burnout, or failure to maintain or refuel your POS, means either losing everything or paying for dead weight every month.
To summarize, I deal with burnout in a couple ways:
1. I don't worry too much about maximizing profit. If I don't feel like re-stocking my factory planets, then I simply don't.
2. I don't run large scale operations. In fact, in everything I've done I started small, and slowly built up my activity until I gained a better understanding of what my limits were. I could obviously be making much more per month if I ran factory planets on 5 additional PI alts, but there is no way I could handle this.
3. I always make sure that I have enough liquid isk on hand to fund all my PVP activities many times over. I don't ever want to run into a situation where I feel that I have to liquidate assets at a loss.
4. I have a couple different isk-making avenues available to me. If I get bored with PI, I might start station trading again. Or I might start running relic sites in null sec again.
5. Probably the most important: I decided long ago that I would just pay for my accounts. I am fortunate that I have the means to do so, and this relieves me of any pressure to PLEX my accounts every month.