It's a wonderful idea on paper, but the stars have to be aligned for it to work. For example, if you have any kids, they shouldn't need a lot from you; your work shouldn't be stressful or mentally taxing and you should be able to leave work behind at 5pm; you shouldn't have any hard relationship problems; or sick family members to take care of.

In other words, you have to be in top emotional and mental shape to pull this off.

I developed software for small clients; but if I had problems at my 9-5, I focused on that, but not always. This resulted in having my boss yelling at me and my clients being exasperated for not having the full-featured software ready. I had fear at work because I didn't want to confront my boss and I developed a fear of answering the phone. It felt like everyone wanted something from me, and RIGHT NOW. Getting a call from my wife or a family member, let alone a friend or a stranger in the middle of this fiasco was almost impossible; I didn't have the emotional resources to handle it all. Sometimes I just broke down and cried. I was ashamed of my performance, and it brought me incredible anxiety 24/7. I had these mountains of work to do, and I felt resentful and didn't want to work on them. All this brought the worst in me.

Looking back on it, I had a hilariously maladaptive "coping" technique: When I got a call from an exasperated client, asking "when will it be ready?" I said "It will be ready tonight", trusting my ninja coding skills. Trust me, after working 8 hours, commuting, and dealing with other people's emotional problems, your working IQ decreases by at least 40 points. I said to myself "I will not sleep tonight, finish that feature, and the client will be OK for at least a couple of weeks." So of course, I wasn't finished with the feature by 5am, and even my young 30-year-old body screamed for rest, and I fell asleep on my chair, or the reclining sofa where I often worked. The next day, I went to work with red eyes, on autopilot, could not get anything done (more work for later!), and the client called again, and I promised "it'll be done by tomorrow", and the cycle continued. It sounds so stupid, but emotionally I was indebted with the client: I couldn't finish the stupid feature that would take me 2-3 hours to finish when fresh, and I felt that I was a subpar programmer if I couldn't ship the damn thing TONIGHT, so I continued to put myself in this state, until the weekend came, and I finished the features on Sundays, most often.

Maybe it was my ADHD: I excel when I only have to focus on one task. But I have a feeling that that might be true for a lot of people too.

Maybe it was a lack of discipline. As the article mentions, to be successful at this you have to say "no matter what happens in my full-time job, or with any personal problems, I will have to continue working constantly on the freelance project." Well, life happens, and when you're this constrained, you have to make hard decisions every day: should I help my wife tonight and work twice as hard tomorrow to compensate? or should I just say no to her and deal with the potential ramifications later?

Sometimes you just want to wind off and relax after work, do something different, say, read a book or have sex. Again, when you're this constrained, it's easy to lose balance and fall if you get distracted. Perhaps you've underestimated the amount of work to do and you learned a lesson in software estimation. But the responsibility is still yours.

Needless to say, I hurt myself a big deal in the process, telling myself that if I quit "I didn't want it enough." When I stopped that madness and started to focus on my 9-5 again, my life became livable again.

However, when I think about the fact that I wasn't successful freelancing it still hurts my ego.

Now, bootstrapping an idea while working full-time is perhaps a bit saner: no one is going to scream at you if you don't hit your deadlines and the motivation is intrinsic. You might never get that startup to fruition, but at least you won't kill yourself in the process.