I haven't seen any statistics about that. But for the projects that are becoming successful, you define what's success to you and they also have their own definition of success.
And for individuals, IMHO and own stats, I think we're more that have sold at profit and even those who have sold lower, they're still in profit upon selling.
There's no exact number or percentage about it.
I think so too, no number of percentages can be stated with certainty about this. It is about how you manage and carry out any form of trade or investment. When it comes to percentage gain or loss, everyone can feel it by their own hard work and failure. But how certain the percentage is cannot be defined well, because the percentage of each profit and loss will vary. Unless you count it from the initial capital with the profit you get, maybe it can be defined. However, before you try it for yourself, you will not know what the percentage gain and loss will be.
Success and failure can happen at any time. Success is earned by your own hard work, and failure is earned by your own fault. The one who increases the percentage of that is you. So try it first, without having to think about the percentage first. Make sure you already have the skills to trade or invest, at least you have the basic skills to do it. Thinking about a percentage of it is a waste of time, and will leave you hesitating. If you are told of a large percentage of profit, you may very well take the initiative to make a trade, but it is not about the percentage of success. The percentage of success is just a measure, which makes it go up or down is the way you do it. Think in advance of the percentage of failure you will experience if you start trading right away, you should be prepared to lose the money you have traded. Because if you fail, all your money can be lost (forfeited). If all you think about is success, I am sure you will be very disappointed if what you find is failure.