I'm sure that most of us don't say it was possible but likely it was impossible because we thought that $7 is a very small amount. In fact, having started with $100 is pretty to grow it, how much more for $7 and it made for 15 days? Certainly, nobody will be able to believe it and give a thumbs up, but doubts. Because even we have a long trading experience, doing it instantly is impossible. Of course, we can earn somehow and grow it but not that fast.
I think this is where the human psychology comes in. There's a bad side and also a good side. The good side is that, when the stake is too high and seems impossible to do, people tend to put more effort to it than they would do to those that are doable easily. And I have done some research on this and this is what I have found. When the numbers are at random, our mind tries to remember it and we think about it more. Thus, it becomes important to us. Add a reason behind it, and that becomes your goal. So what OP did was maybe a psychological game.
Best example for this is to set a time like 10:37 or 9:28 It should never be a round figure like 10:40 or 9:30. Apply this and see for yourself what happens next. You will be on time most of the time.
Now to the bad side. The failure to reach your goal will make you emotional, and it will hurt you in the long run. And you can not set any lower target. Because it will ruin the whole concept. So what we need to learn if we want to do this is emotion control. Then you will be happy no matter the profit amount. Because you know you have worked based on your skills, and you have gained what is possible to do.
Other than this, I have no explanation on this. IF you agree to this, then let me know.