I now have no idea whether this is INTJ-specific, but success usually comes with a certain degree of self-discipline. Whether it is solving a problem or achieving set goals well before the deadline, the personal attitude is important in any case. My parents have recognized this from the beginning and never exerted pressure in their parenting: imposed discipline is never as effective as self-imposed. This affects practically all areas of life and should also be responsible for my saying "if I want something, then I simply do it" - because "simply" is usually understating and you need a lot of willpower to push it through. One could also pin it on a certain degree of autism if you are breeding so intense and for a long time on a problem, trying one possible solution after another, until you finally get it right. While doing that, you lose your sense of time and don't notice the many hours you have invested in the problem.
Even if this autistic-based absolute focus doesn't apply, the personalities are very different when dealing with personal temptations. If you see such people as in the picture, then you have to ask yourself whether you really have to meet every emerging desire.
I have experienced this myself because I noticed last autumn that my manly breasts started to wobble when I ran down the stairs. That was not that much weight - 72kg at 179 cm (i am just a linnet), but this seemed to much. If I than made the decision to change something in this situation, it is simply doing it. Food consumption reduced to a sparse flame and a resulting loss of 2 kg per week. A few weeks later, I reached my 63kg target weight and if I now alternate one day normally eating three meals and the other only half that, i hold that weight. The great realization is just this: That is not fun, but it has to be. And if it has to, you have to suppress your superficial desires. Some people are able to do that, and some not.
This is not much different at work: one can follow the approach that one's 35 or 40 hours is enough and ignore the remainder. But with a position like that you get not far, especially as an entrepreneur. Here is my motto: what has to be done, must be done, pleasure is when there is time for it. It is, of course, a personal consideration: whether I am saying to my client, "I don't have time now, you have to wait" - and get the disadvantages for the future buisiness relationship - or whether I sacrifice my spare time and satisfy my customer first and get the benefits.
I put that to the test in the last weeks: I had set myself as a goal, going to the steam modelers meeting in Zurich with the finished third goods wagon and new-designed transport supports that everything arrives without damage. I've noticed a few weeks before that the whole operation comes to a close call and increased the pace accordingly. As I said before, work and private life are intertwined if you are entrepreneur and I have been able to divert some time in favor of this goal. In the end, professional and private work together ended up around the 100-hour-per-week mark. And that means that you can work, sleep, eat (often only nibbles because it's faster) and some body care but nothing else. The setbacks hit: first my marking tool broke, then the whole locomotive licked like a Swiss cheese during the pressure test because of the regulator. The corresponding pin was jammed so that I had to dismantle a lot more parts than usual, using a lot of brute force because of corrosion, resulting in a need of additional repairs. After the test run was finally successful, the metal circular saw broke and I had to cut everything with the angle grinder manually. Of course, while doing that one sliver flew into my eye despite safety goggles. So if everything goes south, takes longer and is more complicated than planned then you have to bite the bullet. In short: I managed it despite all the adversities and had a half-day left. Likewise, I pulled such actions purely at work. Perhaps that is just the need to prove to all and yourself that you are still the toughest gorilla in the cage and able of such efforts when necessary. However, unlike many Japanese I have no desire for Karoshi (death by overwork), so it is clear from the beginning that you sleep when you are tired and the effort is only temporary.
What is really annoying when you realize that you are the only one who approaches such goals with such determination. Empathy may not be my strength, but if someone pursues a goal from which I also profit, then I help him and make it my goal too. My usual experience was the contrary: when its going into overtime, other people leave and switch to more personal interests. INTJs are usually lone fighters, but from my point of view not decidedly. I would like nothing more than working in a team where you work together towards the goal - and with the same determination as described above. If the team members do not do justice to this claim, it is only logical that this is not really a team and you are better off alone.
The other problem with teamwork is - my team members normally hide behind disability - "I can not do that". This is especially sad when you consider that I usually don't have the abilities when I start with something, I learn on the way. But the determination to simply learn what you need most people lack in my opinion. And again it's true: You are not really a team if you don't share the task. If you cannot do a complex part of the task then you can compensate for this with more work on the simpler parts, but if this also doesn't happen ...