Advice to second attempt applicants
Great posts from flapsupdown and holdmetight.
I've found that successful candidates come from a wide range of backgrounds, professions and age groups. To think that a particular type of candidate will be successful is just a limiting belief. From the candidates that I have known to be successful, it clear to see that they are very committed, and have been well prepared for every stage of the test. They often get caught out on technical questions, but it seems to be equally important that a candidate can accept correction and advice. Airlines want cadets that are easy to train and can learn from mistakes, so become someone that is easy to train.
I'd also add unless you are a native speaker you should start improving your English early. This is essential throughout every stage of the selection process (and your career), not just the ICAO test. Don't think, "hey, I got to stage 1b - now I should start improving my English" because that's going to put your teacher in a more difficult position. It's still possible to improve but it's not going to be as effective as a long term plan. Better English will also help you in every other aspect of your life.
If an assessor asks you to explain eg how a jet engine works, or the difference between various control systems they are assessing your ability to communicate in English, as much as your technical knowledge. I'd say that candidates from a non-technical background may even have an advantage over CPL holders there, in that the assessor's expectations will be lower.
There is also the case where an aviation career might not be right for you, and I can understand that this might be a painful decision, especially if your heart is in it. It's important to consider whether you (a) have the basic aptitude, and (b) have the interest and passion. If you don't have these things then it's ok to move on. Plenty of other people have made the same decision. Rather than work on the skills that you lack, it might be better to leverage the skills that you already excel at. There's a great book called Strengthsfinder 2 that can help you find these. Highly recommended.
If you do have the interest then do try again. One of the great things about aviation is that it's something that you can pursue privately and it's becoming more accessible, so a rejection from an airline is no big deal. Cadet entry is not the only way to an airline career, and you might find that you can get your aviation "fix" through private flying.